Preheat the oven to 350°F (175°C or 165°C for a fan oven).

Grease or line a 12 cup muffin pan.

Make the streusel by cutting the butter into the flour using a pastry cutter or two knives (or a food processor).

Stir in the sugar, cinnamon and rolled oats. Set aside.

For the yogurt muffins - Sift the flour, baking powder, baking soda, cinnamon and salt together in a large bowl.

Stir in the sugar.

Whisk the yogurt, eggs and oil together in a smaller bowl.

Add the yogurt mixture to the dry ingredients all at once.

Stir together until just combined. Do not beat.

Divide the mixture between twelve muffin cups.

Sprinkle with the streusel mixture.

Bake for 15 to 20 minutes or until a skewer inserted in the centre of a muffin comes out clean.

Serve warm.

The muffins will keep in a sealed container for up to 3 days.