For buckle, place water, 64 oz (13 1/2 cups) Krusteaz Professional All Purpose Muffin Mix, softened butter, vanilla, almond extract and eggs in mixer bowl.
Using a paddle, mix on low speed 30 seconds. Scrape bowl and paddle.
Continue to mix on low speed 1 minute.
Scale batter into prepared full sheet pan. (For increased volume, use prepared cake frame.)
Spoon mixed berries and peaches over batter.
For streusel topping, place 8 oz (1 1/2 cups) Krusteaz Professional All Purpose Muffin Mix, oatmeal and sugar in mixer bowl. Stir until blended.
Sprinkle streusel over fruit in pan. Drizzle melted butter over streusel.
For convection oven, bake at 300°F 40-45 minutes; for standard oven, bake at 350°F 55-60 minutes. Drizzle with icing, if desired.