Break 4 eggs and add sugar in a bowl, then whisk for 3 minutes. Add salt then milk gradually, while whisking. Slowly add flour while continuing to whisk. Add melted butter and whisk until batter is smooth, then let rest for 15 minutes. Pour batter on a baking sheet lined with greased parchment paper. Bake at 420F/225C for 25 minutes. Cut in rectangular slices. Serve warm with berry jam, fresh berries and/or cream.