Bring milk, egg whites and butter to room temperature. Preheat oven to 350 degrees and prepare muffin tin with paper liners. Mix milk, egg whites and vanilla together in small bowl and set aside. Mix flour, sugar, baking powder and salt together in bowl of electric mixer. Add butter and mix on low until mixture looks like moist crumbs. Add half of milk mixture and mix on low until combined, then add remaining half and continue to mix on low until just combined. Divide batter equally among prepared muffin tins. Bake for about 15 min., until a toothpick inserted into the center of a cupcake comes out clean. Allow cupcakes to cool completely, then poke several holes down into the cupcake using a chopstick or fork. Carefully spoon 2 tsp. of syrup into the holes in each cupcake. Top with frosting or whipped cream and serve.