Preheat oven to 350°F. Place granola bars into food processor or blender and blend until finely crumbled. Add half of the crumbs to a bowl with flour, melted butter, and brown sugar. Stir to combine. Reserve remaining half of granola crumbs for topping. Press the butter-crumb crust mixture into an 8x8-inch pan lined with parchment or foil. Bake for 10 minutes and allow to cool.