Preheat the oven and skillet: Place a 10-inch cast-iron or oven-safe skillet on the middle rack. Preheat the oven to 425°F (220°C) with the skillet inside.
A hot pan gives the Dutch baby its signature puff.
Blend the batter: In a blender, add eggs, almond flour, coconut flour, almond milk, heavy cream, sweetener, vanilla, cinnamon, and salt. Blend on medium until smooth, about 20–30 seconds. You can whisk by hand, but blending yields a lighter texture.
Rest briefly: Let the batter sit for 5 minutes so the coconut flour hydrates.
This prevents a thin, watery texture.
Melt the butter: Carefully remove the hot skillet and add the butter. Swirl until melted and the pan is coated. Work quickly so the butter doesn’t burn.
Pour and bake: Give the batter a quick stir, then pour it into the buttered skillet.
Return to the oven immediately and bake for 14–18 minutes, until puffed and deep golden around the edges.
Serve right away: The Dutch baby will deflate a bit as it cools. Slice, top with berries, a squeeze of lemon, a dusting of powdered sweetener, or a dollop of whipped cream, and serve warm.