Prepare the crumble dough. Mix the hazelnuts to obtain a coarse powder. Mix it with your fingertips with the flour, sugar and butter until you get the consistency of coarse sand. Place in the fridge.
Preheat the oven to 180 ° C (th.6).
Whisk the sugar and egg until the mixture whitens. Mix the flour, baking powder and salt, add them to the egg. Melt the butter and pour it into the mixture. Add the milk, mix well. Finally, gently add the raspberries.
Fill muffin cups with dough up to ¾ of the height. Sprinkle the cold crumble dough over it.
Bake for 25 to 30 minutes until the muffins are golden brown. On leaving the oven, let them cool on a rack.
Serve them alone at tea time, or with a vanilla ice cream for dessert.