Gather the ingredients. Preheat the oven to 375 degrees F (190 degrees C).

Make crumble: Combine flour, sugar, baking powder, and salt in a large bowl. Whisk until thoroughly combined. Grate in frozen butter, stopping occasionally to toss butter into flour mixture until coated.

Stir in egg yolks and vanilla with a fork until egg is mostly absorbed. Add 1 teaspoon vinegar; mix briefly. Use your hands to finish mixing, squeezing until clumps form, but mixture remains mostly dry. Add more vinegar if needed. Set crumble aside.

Make filling: Combine blueberries, raspberries, and blackberries in another large bowl. Add sugar, cornstarch, lemon juice, lemon zest, and cayenne pepper. Mix until well combined and sugar and cornstarch are mostly dissolved.

Place about 1/2 of the crumble mixture into the bottom of a 2-quart baking dish. Press mixture down using a flat cup until well compacted. Spread berry filling on top. Sprinkle remaining crumble mixture over berries, squeezing some of the crumble into clumps.

Bake in the preheated oven until top is beautifully browned and berry filling bubbles, 40 to 45 minutes. Let cool to room temperature before serving, about 30 minutes.