Step 1

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

Step 2

Combine flour, salt, baking powder, and sugar in a bowl. Whisk until thoroughly combined. Grate in the frozen butter, stopping occasionally to toss the butter into the flour mixture until coated. Drizzle in vanilla extract; add egg yolks. Stir with a fork until egg is mostly absorbed. Add vinegar; mix briefly. Use your hands to finish mixing, squeezing until clumps but mixture remains mostly dry. Add 1 teaspoon vinegar if needed.

Step 3

Combine blueberries, raspberries, and blackberries in another bowl. Add lemon zest, lemon juice, sugar, and cornstarch. Sprinkle in cayenne pepper. Mix until sugar and cornstarch are mostly dissolved.

Step 4

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 the berries over the crust. Sprinkle the remaining crumble mixture on top, squeezing some of it into clumps.

Step 5

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