In a medium bowl, cream the butter and brown sugar together using an electric mixer, food processor, or a fork until well combined.
Add the chopped nuts, lemon juice, cinnamon, flour, and salt.
Stir or pulse until the mixture is combined and looks like coarse, crumbly sand. It should not form a solid dough.
Crumble the mixture over your favorite crisp, quick bread, or muffins before baking. Alternatively, bake on a sheet pan at 350°F / 175°C until golden brown to use as a crunchy topping for yogurt or a filling for crêpes.