Cream the butter and sugar and add one egg at a time. Combine the flour and baking powder and sift into the mixture. Add some milk to the batter until it has a sticky thick consistency. Add the chocolate chips, roasted hazelnuts and 3/4 of the blueberries.
Cook the remaining blueberries in a small saucepan with a very small amount of water over small heat. Let the berries pop and mash with a spoon. Add to the batter (you could sift it, I just put the whole thing in).
Fill muffin cases to 3/4 full.
For the crumble rub some butter into some brown sugar. Add the flaked almonds, cinnamon and flour to give you a crumbly texture. You dont have to be exact here just aim for a crumbly not to sticky mixture. Sprinkle over the batter in the muffin cases and bake for 20-30 minutes at 180°C Fan (our gas oven is a bit dodgy so I cant give you an exact time here :/).
The muffins should have a wonderful golden colour on the outside and a toothpick should come out clear.