Preheat oven to 425 °F. Preheat a 12-inch cast iron skillet in the oven so it gets nice and hot.
For batter, melt two tablespoons butter and add to a blender with eggs, 2 tablespoons sugar, milk, vanilla, and flour. Blend until smooth, about a minute.
Slice peaches into thin slices. When cast iron skillet is hot, remove it from oven (careful!) and add two tablespoons butter to the skillet along with a tablespoon of sugar. Stir to combine. Lay peaches out on the skillet in an even layer.
Pulse batter one more time to make sure it’s combined and immediately pour batter into hot skillet over peaches.
Bake dutch baby in oven for 20-22 minutes until edges are browned and cracking and center is puffed.
Remove pancake from oven and dust with powdered sugar. Serve while warm with berry syrup.
For berry syrup: Combine berries with syrup and butter in a small pot over low heat. Heat until butter is melted and berries just start to break down, just a few minutes. Then remove from heat. Spoon over dutch baby slices while serving.