Sift cake flour and almond flour into a bowl, then add sugar.

Mix thoroughly using a whisk.

Add cold diced butter (1cm cubes) and mix using a scraper.

Rub the mixture with your palms until it forms small crumbs.

Refrigerate the crumble until ready to use.

For the cake, cream softened butter until smooth, then add sugar and mix well.

Gradually add beaten eggs while mixing.

Mix in Nutella until evenly combined.

Sift cake flour, baking powder, and cocoa powder into the mixture, then add milk and vanilla extract.

Add chocolate chips and mix until just combined.

Grease muffin tins with melted butter.

Fill each tin with 2 tablespoons of cake batter and smooth the surface.

Sprinkle crumble over the batter until fully covered.