In a medium mixing bowl, whisk to combine the egg yolks, milk, brandy, and melted butter. Sift in the flour, sugar, and salt. Combine well using a whisk, and chill for at least 1 hour.
Heat oil in a large nonstick or cast-iron skillet over medium heat. Beat the egg whites until stiff but not dry, using a whisk. Fold egg whites into the batter using a rubber spatula.
Slice apples into 1/4-inch-thick slices; discard the first and last slice of each apple. Dip the apple slices into the batter to coat. Remove with a fork, and gently place in the heated oil. Cook in small batches until deep golden in color, about 1 1/2 minutes per side. Transfer to paper-towel-lined plate. Serve immediately with a sprinkling of sugar or a drizzling of maple syrup.