Mix everything but butter together: flour, brownsugar, pecans, and cinnamon.
Add melted butter.
Using a fork, gently stir and fold until clumps form.
Make sure to evenly stir together the mixture so no flour patches remain hidden in a clump.
Add this streusel topping on top of your muffin batter, bread batter, etc. before baking. You *may* need to add a few extra minutes to your bake time to account for the added topping.
For larger crumbs, use roughly chopped pecans and stop stirring once large clumps form.For smaller crumbs, use finely chopped pecans and continue to stir and break up larger clumps.