Put butter in a 9-inch pie pan. Place pan in the preheating oven until butter is melted, 5 to 10 minutes.
Whisk flour, milk, eggs, white sugar, and salt together in a bowl; pour mixture into the hot butter.
Bake in the preheated oven until pancake is brown on the edges and a toothpick inserted in the center comes out clean, 20 to 24 minutes. Squeeze lemon over pancake and sprinkle with confectioners' sugar.
