oat streusel topping
First, let's make Oat Streusel Topping. In a small bowl stir to combine rolled oats, sugar and all-purpose flour. Using your fingertips lightly rub the butter into the mixture, to get a nice crumb. Set aside until needed. Preheat your oven to 180 °C / 355 °F.
Blueberry muffins mixture
In a bowl combine all-purpose flour, finely ground oats, baking powder, and sugar. In a separate bowl, cream the softened butter, then add the eggs and mix using an electric mixer to get a smooth mixture, for about 2 minutes. Add plain yogurt, mix to combine, then add the flour mixture and mix to combine well. Gently fold in the blueberries (fresh or frozen) using a spatula.
bake and serve
Spoon the batter into liners, filling them about 2/3. We used an ice cream scoop, which worked amazingly. Top with oat streusel and place in the preheated oven. Bake for about 25 minutes (or until a toothpick inserted in the center comes out clean) at 180 °C / 355 °F. Allow the muffins to cool for 15 minutes in the muffin pan, then transfer to a wire rack to continue cooling. Enjoy. Store in an airtight container for up to 3 days.