Preheat oven to 300 degrees F/150 degrees C.

Place dry ingredients such as all-purpose flour, sugar, and chopped nuts in a medium bowl. Optionally add spices and mix. Add cold butter, cut into cubes, and work with your fingertips until you get coarse crumbs. The texture will look like wet "sand." 

Try to "sand" the dough quickly not to heat the butter. Crumbling the dough with fingers makes the butter crumb less uniform and delicious. Alternatively, you can mix the crumble dough in a food processor or a stand mixer fitted with the paddle attachment. Or you can work all the ingredients with a rubber spatula, a fork, or a pastry blender. Then use a unique tool - spaetzle maker - or spider skimmer with large holes to grate the streusel dough. Drop the filaments on the baking sheet and spread them out. Or form a dough ball and chill it in the refrigerator for 1 to 2 hours. Then grate the dough using a grater with large holes. This version gives the dough a thicker consistency.

Spread the crumbles on a baking sheet lined with parchment paper and bake for 20 to 25 minutes or until the desired color. Let cool. Or sprinkle the crumble topping on top of muffins, cake, tart, pie, etc., and bake as directed in the recipe.