Make this once or twice a year (doubling or quadrupling the recipe) so you always have ready-to-use streusel topping for these muffins, or sour cream coffee cakes, yeasted bubkas or quick breads

Place walnuts, brown sugar, flour, cinnamon, nutmeg, salt and vanilla in work bowl of a food processor (if processor is too small, do half a batch at a time). Pulse briefly to combine. Add in butter chunks and process to make a coarse, crumbly mixture. Place in the freezer. Freezes almost indefinitely.