Caramelized Onion Pasta with Chilli

This caramelized onion pasta with chili oil transforms simple ingredients into something extraordinary. The sweet depth of slowly cooked onions pairs perfectly with the vibrant heat of homemade chili oil, creating a pasta dish that feels both comforting and exciting.

I first made this dish during a particularly busy week when I needed something impressive without a grocery run. The magic that happens when onions slowly transform and release their natural sugars has made this my go-to recipe whenever I want to wow dinner guests without excessive effort.

Ingredients

• 12 oz pasta of your choice: The substantial base that carries all those wonderful flavors. Longer shapes like spaghetti or fettuccine catch the oil beautifully.
• 2 large onions: The star ingredient that transforms through slow cooking. Look for firm onions with tight, papery skin for best results.
• Olive oil and butter: The combination creates the perfect medium for caramelizing onions. The butter adds richness while olive oil prevents burning.
• Sugar: Optional but helpful for speeding up caramelization. Just a teaspoon creates that beautiful browning.
• Chili flakes: Provides the essential heat. Fresh, bright red flakes offer the best flavor and color.
• Fresh garlic: Adds aromatic depth to the chili oil. Choose firm cloves without green sprouts.
• Smoked paprika: Optional but adds wonderful complexity and smoky notes.
• Parmesan cheese: For serving. Freshly grated provides the best flavor and melting quality.

Step-by-Step Instructions

Caramelize the Onions:

Slice onions thinly and uniformly to ensure even cooking. Heat olive oil and butter in a large skillet over medium-low heat until butter melts completely. Add onions with a pinch of salt, spreading them evenly across the pan. Cook for 25-30 minutes, stirring every 5 minutes or so. The key is patience here. You'll see them gradually transform from sharp and pungent to sweet and golden brown. If they start to stick, add a tablespoon of water to release the fond from the pan bottom. The optional teaspoon of sugar helps accelerate browning but isn't necessary if you have time.

Prepare the Chili Oil:

While onions are caramelizing, make your chili oil. Heat olive oil in a small saucepan over medium-low heat. Add minced garlic and watch carefully to avoid burning. When garlic becomes fragrant after about 30 seconds, add chili flakes, letting them sizzle gently in the oil for 1-2 minutes. The oil will take on a beautiful red hue as the chili infuses. Add smoked paprika and salt, stir to combine, then remove from heat. The residual heat will continue to develop flavors as it cools.

Cook the Pasta:

Bring a large pot of water to a rolling boil. Add enough salt to make it taste like sea water. This properly seasons the pasta from within. Add pasta and cook according to package directions until al dente. Before draining, reserve about half a cup of the starchy cooking water. This liquid gold helps bind the sauce to the pasta. Drain pasta but do not rinse to preserve the starchy coating that helps the sauce adhere.

Combine Everything:

Return the skillet with caramelized onions to medium heat. Add drained pasta directly to the onions, tossing continuously to coat each strand. Add a splash of reserved pasta water, which will create a silky sauce as it combines with the onions and residual fat. Pour most of the chili oil over the pasta and toss again. The vibrant red oil should coat everything evenly, creating beautiful color contrast with the golden onions.

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The caramelized onions are truly the heart of this dish. I discovered their transformative power years ago when making French onion soup, and now I incorporate them whenever possible. The patience required to slowly cook them pays off enormously in the deep, complex flavor they develop.

Make Ahead Options

This pasta actually benefits from some time for flavors to meld. You can caramelize the onions up to three days ahead and store them in an airtight container in the refrigerator. The chili oil can be made up to two weeks in advance and kept at room temperature in a sealed jar. These make-ahead components turn this into an incredibly quick weeknight meal when you just need to boil pasta and assemble.

Perfect Pairings

This pasta works beautifully alongside a simple arugula salad dressed with lemon and olive oil. The peppery greens and bright acidity balance the rich, sweet onions and spicy oil. For wine, reach for a medium-bodied red with good acidity like a Chianti or Sangiovese that can stand up to the flavor intensity without overwhelming it.

Customization Ideas

The basic formula here is incredibly adaptable. Try adding a handful of spinach or arugula in the final toss for freshness and color. For protein, consider adding Italian sausage, pancetta, or chickpeas for vegetarians. A sprinkle of toasted pine nuts adds wonderful texture, while a dollop of ricotta or mascarpone cheese creates a creamy variation that tempers the chili heat.

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This pasta is a masterclass in coaxing big, bold flavors out of humble ingredients. Worth every minute!

Frequently Asked Questions

→ How long does it take to properly caramelize onions?

Properly caramelizing onions takes 25-30 minutes over medium-low heat. This slow cooking process allows the onions to develop a deep golden-brown color and rich, sweet flavor. Rushing this step will result in sautéed rather than caramelized onions, so patience is key for the best flavor development.

→ Can I make the chilli oil ahead of time?

Yes, the chilli oil can be made up to two weeks ahead and stored in an airtight container in the refrigerator. In fact, making it in advance allows the flavors to develop and intensify. Just be sure to bring it to room temperature before using, as the oil may solidify when chilled.

→ What type of pasta works best with this dish?

Spaghetti, fettuccine, or penne all work well with this dish. Long pasta shapes like spaghetti or fettuccine are ideal as they catch the chilli oil nicely, while penne captures bits of caramelized onion inside the tubes. Choose based on your preference, as the flavors complement any pasta shape.

→ How can I adjust the spice level?

To adjust the spice level, simply modify the amount of chili flakes in the oil. For a milder version, use 1-2 teaspoons instead of a full tablespoon. For extra heat, increase to 1½ tablespoons or add a pinch of cayenne pepper. You can also serve additional chilli oil on the side, allowing each person to add spice to their own preference.

→ Can I make this dish vegan?

Yes, this dish is easily adapted for vegans. Simply replace the butter used for caramelizing onions with additional olive oil or plant-based butter. Skip the Parmesan garnish or use a vegan cheese alternative. The core flavors of caramelized onions and chilli oil will remain delicious without any animal products.

→ Why is reserving pasta water important for this recipe?

Reserving pasta water is crucial because it contains starch that helps sauce cling to pasta. When added to the caramelized onions and pasta, this starchy water creates a silky consistency that helps distribute flavors evenly. It also prevents the dish from becoming dry, especially when reheating leftovers.