Lightly-Topped Peach-Blueberry Crisp

16 ounces frozen blueberries, defrosted (2 1/4 cups)

1/2 teaspoon almond extract

1/3 cup granulated sugar

1 tablespoon cornstarch

1/4 cup quick-cooking or regular oatmeal (do not use instant oatmeal)

1/2 cup flour

1/3 cup light brown sugar

1/2 teaspoon ground cinnamon

1/2 teaspoon freshly grated nutmeg

3 tablespoons cold salted or unsalted butter, cut into small cubes