In a small bowl, toss the blueberries with 2 tablespoons of sugar and set aside. Let sit for at least 30 minutes, stirring occasionally.
Meanwhile, preheat the oven to 350 degrees and position a rack in the center. Rub the inside of a No.8 Field Skillet all over with butter.
In a mixing bowl, combine the milk, eggs, flour, lemon zest, vanilla extract, salt, and the remaining 1 cup of sugar until smooth. Pour about a third of the batter into the skillet, then transfer to the oven and bake for 15 minutes, or until the batter is almost set but still jiggles a little in the middle.
Remove the skillet from the oven. Sprinkle the blueberries in an even layer over the cooked batter, then pour the remaining batter over the fruit.
Return the skillet to the oven and bake until the clafoutis is set and a cake tester inserted into the center comes out clean, 45 minutes to 1 hour. Let cool until ready to serve (the clafoutis is best served warm or at room temperature); dust with confectioner’s sugar (if using) just before serving.
Notes
