Heat the oven to 180C, 160C fan, 350F, Gas 4.
Oil and line a baking tin – a 20cm x 30cm tin works well for these quantities.
Sift the flour and baking powder into a bowl and add the oats and caster sugar.
Beat the melted butter, eggs and yoghurt together. Add to the dry ingredients and mix well.
Pour into the prepared tin and smooth evenly, then scatter with the raspberries.
Make the topping by rubbing the butter into the flour then stir in the rest of the ingredients.
Sprinkle over the raspberries.
Bake for 20 to 25 minutes until risen, set and golden on top.
Cool in the tin, then cut into squares and enjoy!
You can also make this recipe with strawberries or blueberries using the appropriate yoghurt.