In a bowl mix the cubed cold butter, brown sugar, salt, flour, oats, and cinnamon. Use either your hands or a pastry cutter. Once the mixture is combined well and has small clumps, set aside in the fridge for later.
½ cup all-purpose flour, ¼ cup oats, ⅓ cup brown sugar, ½ teaspoon cinnamon, ½ teaspoon salt, ¼ cup butter