Whisk together the breadcrumbs, chocolate sprinkles, hazelnuts, flour, cacao, and baking powder.
Cream together the butter and brown sugar, about 2-3 minutes.
Add the eggs one at a time. Wait until each is thoroughly combined before adding the next.
Turn the mixer speed down to low. Add the dry mixed ingredients in thirds until fully combined.
Scrape the batter into the prepared loaf pan.
Bake on the middle rack of the oven for 30 minutes.
Make the brown sugar streusel:
Place the butter, brown sugar, and flour into a bowl. Use your fingers or a large fork to rub the mixture together until combined.
Sprinkle the salt over the mixture, and add a pinch of nutmeg.
Continue to combine until the mixture forms large crumbs.
Remove the cake from the oven.
Spoon the streusel over the top.
Return the cake to the oven for another 15-20 minutes or until a knife inserted in the center of the cake comes out clean.
Let cool for 20 minutes.
Run a butter knife along the sides of the pan.
Gently remove the cake from the pan and transfer to a wire rack to cool completely.
Transfer to a platter. Slice and serve.
Recipe Notes
*To make hazelnut flour, place raw shelled hazelnuts (you can leave the skins on) in a food processor or blender together with a tablespoon of powdered sugar. Pulse until the hazelnuts are completely pulverized and no large pieces are left. The texture should resemble coarse flour. The powdered sugar prevents the nuts from forming a paste. If it looks like this is happening, add more powdered sugar one teaspoon at a time.