Ingredients
1/2 cup all-purpose flour
1/4 cup granulated sugar
3 Tbsp. unsweetened cocoa
1/4 tsp., plus a pinch kosher salt, divided
3 large eggs, at room temperature
1 cup whole milk, at room temperature
1 1/2 tsp. vanilla extract, divided
2 Tbsp. unsalted butter
1/2 cup heavy whipping cream
2 Tbsp. powdered sugar
1/4 tsp. ground cinnamon
1/2 cup sliced fresh strawberries
1/2 cup fresh raspberries
Flaky salt, to taste (optional)
Directions
Place a 10-inch cast-iron skillet in oven with rack in lower third position. Preheat oven to 425°F. (Do not remove skillet while oven preheats.)
Whisk together all-purpose flour, granulated sugar, cocoa, and 1/4 teaspoon of the salt in a medium bowl. Whisk together eggs, milk, and 1 teaspoon of the vanilla in a medium bowl until well combined. Gradually whisk about half of the milk mixture into flour mixture until smooth. Gradually whisk in remaining milk mixture until thoroughly combined.
Carefully remove hot skillet from preheated oven; add butter, and swirl to melt and coat skillet. Working quickly, pour batter into skillet. Bake in preheated oven until puffed and brown around edges, 18 to 22 minutes.
Meanwhile, whisk together heavy cream, powdered sugar, cinnamon, and remaining 1/2 teaspoon vanilla and pinch of kosher salt in a bowl until soft peaks form, 45 seconds. Chill, covered, until ready to serve.
Remove Dutch baby from oven. Top with whipped cream and berries; sprinkle with flaky salt, if using. Serve immediately.