- To make the butterscotch sauce, in a heavy-bottomed saucepan, melt the butter over medium heat. Add the brown sugar, cream, and salt and whisk until well blended. Bring to a very gentle simmer and cook, whisking occasionally, until the sugar is completely dissolved and is bubbling, about 5 minutes. Remove from the heat and let cool. Add the vanilla and stir to combine.
- To make the pancakes, in a large bowl, whisk together the flour, baking powder, and salt.
- In a bowl, using a whisk or an electric mixer, whip the egg whites until soft peaks form.
- In another bowl, whisk together the milk, egg yolks, and butterscotch sauce. Pour the milk mixture over the flour mixture and fold to combine partially. Fold in the egg whites just until no visible flour remains; the mixture will still be lumpy.
- In a large nonstick frying pan, melt 1 tablespoon butter over medium heat. Pour in 1⁄3 cup batter for each pancake and sprinkle 1—2 teaspoons chocolate chips on top. Cook until bubbles form on the top, 2 to 3 minutes. Flip the pancakes and cook until golden on the bottom, about 2 minutes longer. Transfer the pancakes to a platter and keep warm in the oven. Repeat to cook the remaining pancakes, adding more butter as needed.
- Serve the pancakes with the remaining butterscotch sauce.