- 3/4 cup butter
- 3/4 cup white sugar
- 1 tablespoon cornstarch
- 1 lemon, zested
- lemon, juiced
- 1 tablespoon vanilla extract
- 4 cups frozen mixed berries, thawed
- 1 cup all-purpose flour
- 1 cup rolled oats
- 1 cup brown sugar
- 1/4 teaspoon baking soda
- 1/4 teaspoon baking powder
- 1/4 teaspoon salt
- Preheat oven to 350 degrees F (175 degrees C). Butter a 9-inch pie dish.
- Melt butter in a small saucepan; bring to a low simmer and cook, stirring frequently, until butter is browned, fragrant, and foamy, with browned bits in it, 5 to 10 minutes. Cool to room temperature, about 15 minutes.
- Combine white sugar, cornstarch, lemon zest, lemon juice, and vanilla extract in a bowl. Add thawed berries and toss gently. Transfer berry mixture to the bottom of the greased pie dish.
- Combine flour, oats, brown sugar, baking soda, baking powder, and salt in another bowl. Stir in 1/2 cup browned butter until mixture is evenly wet and crumbly. Spread evenly over top of berry mixture.
- Bake in the preheated oven until golden brown, 35 to 40 minutes. Remove from oven and allow to cool slightly before serving.