Traditional Crumb Topping

Combine all of the above ingredients in a bowl and rub together with hands until the mixture resembles a nicely textured crumb topping. This can also be made in a 5-quart (5 L) mixer with the paddle attachment or a food processor, but be careful not to overmix. Use immediately, chill in the refrigerator for a couple of days, or freeze for up to 1 month.