1/2 cup old-fashioned oatmeal, uncooked (not the quick-cooking kind)
1 cup unbleached all-purpose flour
1/2 cup firmly packed dark brown sugar
1/2 teaspoon salt
1/2 cup cold unsalted butter, cut into pieces (1 stick)
1 pint blueberries
1 pint heavy cream
1 cup white sugar
1 tbsp cornstarch
Preheat the oven to 350F. Spread the oatmeal on a rimmed baking sheet. Toast until lightly golden and fragrant, 5 - 7 minutes.
In a food processor, add the oatmeal, flour, sugar and salt. Pulse until combined and the oatmeal is chopped. Add the butter and pulse until the mixture forms pea-sized crumbles.
To make cookies: Pat the dough evenly into an 8-inch square baking dish. Bake for 25 - 30 minutes. Remove from pan while still warm and cut into squares or other shapes.
To make crumbles: Pat the dough into an even 1/4 inch layer on a baking sheet. Bake for 25-30 minutes. When cool, break the shortbread into crumbles.
Whip the cream with half the white sugar until it holds its shape.
Toss the berries with the rest of the white sugar and cornstarch and heat in a pan over low heat until thickened slightly.
Layer the cookie crumbles, cream and berries in a glass or mason jar.