Preheat the oven at 340F. Line two trays to bake 12 muffins with paper cases.
Sift the together the flour, baking powder and salt and set aside.
In a mixing bowl whisk the egg with the sugar and the melted butter. Whisk in the milk and lemon zest then gently fold in the berries. Keep a few berries aside to decorate the top.
Add the sifted dry ingredients very gently with a spatula and combine the ingredients but make sure to stir enough to combine enough although some lumps should be visible. Do this by hand!
Spoon the mixture in the muffin cases to fill them up. Cover with the crumble topping and dot with a few extra berries.
Bake for 30-35 minutes or until a skewer comes out clean. Take out of the tray and cool over a rack.
Put the flower, sugar and butter and mix with you hands until you have a uniform breadcrumb consistency. Don't over do it or you will be left with a baking dough. No panic if this happens just make cookies out of it! and restart the process.
Double the recipe and keep the crumble in a ziplock bag up to 3 months.
You can substitute the butter in the muffins with 1 1/2 cup of vegetable oil for a light crumb.
You can also use different fruits, chocolate and nuts combinations. My favorites are white chocolate chips and bananas, pear and fresh ginger or walnut and apples.