Preheat oven to 350°F. Place a tart (or pie) dish or oven safe skillet in the oven with 1/2 Tablespoon butter. Allow pan to heat in the oven and swirl the melted butter evenly to coat the pan, so it's well greased.
Meanwhile, in a blender or bowl using an immersion blender, add milk, eggs, 1/2 cup sugar, vanilla, and lemon zest. Blend well until combined. Add flour and salt. Blend for approximately 1 minute until slightly foamy.
In the hot pan, pour enough batter to coat about 1/4 inch layer of the pan. Let sit for 1-2 minutes until batter is slightly set (this will help the berries remain in the middle). Spread berries in an even layer on the set batter and sprinkle with the remaining 2T sugar. Pour remaining batter on top of berries. If needed, use the back of a spoon to smooth out top.
Bake for 45-55 minutes. The clafoutis center will rise (and deflate as it cools once done cooking). Knife should come out clean when it's done, and the edges golden brown.
Clafoutis is best served warm after baking, but can be served at room temperature or cold. Sprinkle powdered sugar on top before serving.
Notes
For any leftovers, cover and store in the fridge. Reheat at 300°F for 10-15 minutes until warm.