In a large mixing bowl, combine the berries and granulated sugar until evenly coated. Set aside to macerate.
In another large mixing bowl, combine the flour, rolled oats, brown sugar, cinnamon, and nutmeg. Then cut in the butter with a fork or a pastry cutter.
Spread half of the oat mixture evenly over the bottom of a 9-inch x 13-inch baking dish. Spread all of the berries over top. Cover the berries evenly with the remaining oat mixture.
Bake for 30 to 40 minutes until the oats are golden and the berry filling is bubbling.
Remove from the oven and allow to cool for 10 minutes before serving. We like some vanilla ice cream or whipped cream with this berry crisp.