Cake:
• 3 1/2 cups all-purpose flour
• 1 tablespoon baking powder
• 1/2 teaspoon salt
• 2 cups finely chopped chocolate candies such as Snickers, Almond Joy or Reese's peanut butter cups
• 16 tablespoons (2 sticks) unsalted butter, at room temperature
• 1 1/2 cups sugar
• 4 large eggs, separated, at room temperature
• 2 teaspoons vanilla extract
• 1 1/4 cups whole milk, at room temperature
• 1/4 teaspoon cream of tartar

Icing:
• 4 1/2 ounces bittersweet chocolate, chopped
• 1/2 cup heavy cream