Combine the flour, sugar, and salt in a mixing bowl and stir together.
Melt the butter in 20-second bursts in the microwave until fully melted, then pour it into the dry ingredients.
Mix the melted butter into the dry ingredients with a fork until it is evenly dispersed and the mixture clumps together. It should look like very chunky breadcrumbs with some big lumps and some small ones.
Sprinkle the crumble topping over your muffins or fresh fruit and bake according to your recipe instructions. See the post above for ideas on how to use your delicious streusel topping!
Notes
This recipe makes enough crumble topping to sprinkle on 24 muffins or to make an 8x8-inch fruit crumble. For a 9 x 13-inch dish, double the recipe.