01 -
In a large bowl, thoroughly combine packed brown sugar, granulated sugar, ground cinnamon, melted butter and all-purpose flour until a crumbly mixture forms. Set aside or refrigerate to prevent warming.
02 -
Preheat oven to 200°C. Prepare a 12-cup muffin tin with non-stick spray or paper liners and set aside.
03 -
In a small saucepan, combine fresh blackberries, granulated sugar and ground cinnamon. Cook over medium-high heat, stirring and mashing the fruit, until the mixture thickens and is syrupy, about 5 minutes. Allow to cool to room temperature.
04 -
In a large mixing bowl, sift together all-purpose flour, baking powder, baking soda, ground nutmeg, ground cinnamon and salt. Add the rolled oats and mix. Set aside.
05 -
Using an electric mixer or stand mixer with paddle, beat oil and packed brown sugar on medium speed until light and fluffy, about 2 minutes. Add eggs and vanilla extract, beating until well combined.
06 -
In a measuring jug, whisk milk and Greek yogurt or sour cream until smooth. Set mixer to low and alternate adding flour mixture and milk mixture to the wet batter, beginning and ending with flour. Mix until just combined, avoiding overmixing.
07 -
If using, gently fold in pumpkin or sunflower seeds with a spatula.
08 -
Divide batter evenly among the muffin cups, filling to the brim. Top each with one teaspoon of blackberry swirl and use a toothpick to gently create a marbled effect.
09 -
Evenly sprinkle the chilled streusel topping over each muffin.
10 -
Bake for 27–30 minutes until the tops are golden and a toothpick inserted in the centre comes out clean. Cool in pan for 10 minutes, then transfer to a rack to cool completely.