Tarte Tatin-Filled Pancakes

INGREDIENTS

• 1 cup sugar
• 2 Tbs. water
• 4 Tbs. (1/2 stick) unsalted butter, cut into 1/2-inch cubes
• 1 1/2 tart apples, such as Granny Smith or Pink Lady, peeled, cored and each cut into 16 slices, then halved horizontally
• 1 1/4 cups ebelskiver pancake mix
• 2 eggs, separated
• 1 cup milk
• 2 Tbs. unsalted butter, melted, plus more for cooking
• Vanilla ice cream for serving