In a medium bowl, use a pastry cutter, two forks or your hands to combine the oats, butter, flour, brown and granulated sugar, salt, and cinnamon. The butter should be fully incorporated and no sandy patches in the bowl.
1 cup old-fashioned rolled oats, 8 tablespoon unsalted butter, ½ cup all-purpose flour, ½ cup brown sugar, ¼ cup granulated sugar, ½ teaspoon salt, ½ teaspoon ground cinnamon