1. Preheat oven to 350°. Line (12-cup) standard muffin pan with baking cups; spray cups with cooking spray. In large bowl, whisk flour, baking powder, baking soda and salt. In separate large bowl, with mixer on medium-high speed, beat 1/2 cup butter and 3/4 cup sugar 2 minutes or until light and fluffy; add egg whites, 1 at a time, making sure each egg white is fully incorporated before adding next. Add sour cream, 1/4 cup milk and 1/2 teaspoon vanilla bean seeds; beat 30 seconds or until incorporated. Add flour mixture; beat 2 minutes or until incorporated, scraping down bowl occasionally. Divide batter into prepared cups; bake 20 minutes or until toothpick inserted in center of cupcakes comes out clean.
2. In small saucepan, heat 1/4 teaspoon vanilla bean seeds, remaining 3 tablespoons sugar and 3 tablespoons water to a simmer over medium-high heat, whisking occasionally; remove from heat and cool 15 minutes. Makes about 1/3 cup simple syrup.
3. Cool cupcakes 10 minutes in pan on wire rack; poke holes in center of cupcakes with toothpick. Carefully brush tops of cupcakes with simple syrup; transfer to wire rack and cool completely.
4. In large bowl, with mixer on medium-high speed, beat powdered sugar, and remaining 1/2 cup butter, 1 tablespoon milk and 1/4 teaspoon vanilla bean seeds 5 minutes or until light and fluffy, scraping down bowl occasionally. Makes about 1 1/4 cups frosting.
5. Pipe or spread cupcakes with frosting. Makes 12 cupcakes.

Approximate nutritional values per serving (1 cupcake): 338 Calories, 17g Fat, 10g Saturated Fat, 44mg Cholesterol, 126mg Sodium, 45g Carbohydrates, 0g Fiber, 31g Sugars, 30g Added Sugars, 3g Protein