In a medium bowl, stir together flour, ⅓ cup (73 grams) brown sugar, oats, and salt until combined. Using a pastry blender or 2 forks, cut in cold butter until mixture is crumbly. Stir in ¼ teaspoon (1 gram) almond extract. Refrigerate until ready to use.

Preheat oven to 375°F (190°C).

In a large bowl, whisk together cornstarch, remaining ¾ cup (165 grams) brown sugar, remaining ½ teaspoon (2 grams) almond extract. Stir in strawberries, blueberries, raspberries, and blackberries until well combined. Pour into a Milo 10-inch enamel-coated cast-iron skillet. Sprinkle flour mixture in large clumps all over fruit mixture.

Bake until topping is golden brown and filling is bubbly, 35 to 40 minutes. Let cool slightly before serving. Serve with vanilla ice cream.