Grease and flour a muffin pan, or insert paper liners. Preheat oven to 350°F.

Using a countertop mixer fitted with the paddle attachment, cream the butter and sugar on high speed until light and fluffy (2-3 minutes).

In a separate bowl, whisk together the flour, baking powder, salt and lemon zest; set aside.

Whisk together the lemon juice, egg whites, and milk until fully combined.

Add flour mixture to the bowl in 3 additions and liquid mixture in 2 additions, beginning and ending with the flour mixture. Mix on low speed after each addition until fully combined. (Tip: Don’t forget to scrape down the sides of the mixing bowl!)

Fill each muffin cup or liner approximately 2/3 full.

Bake at 350°F for 22-24 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Allow cupcakes to cool before frosting.

Using a small food processor or blender, puree the strawberries until smooth.

Transfer the strawberry puree to a small saucepan, and place over medium-low heat. Cook puree for 15 minutes (or longer—until about ½ cup left), stirring often to prevent it from burning. Remove puree from heat and let it cool completely.

Meanwhile, using a countertop mixer fitted with the paddle attachment, cream the butter on high speed until light and fluffy.

Once puree has cooled, add ½ cup of puree to the bowl; mix until well combined.

Add the powdered sugar, 1 cup at a time, mixing fully after each addition. (Note: The amount of powdered sugar will depend on personal preference and the sweetness of the berries.)

(Optional) Add the lemon juice and mix until fully absorbed. (Note: The lemon juice adds a wonderful tartness that cuts the sweetness of the frosting, if desired.)

If necessary, add milk 1 Tbsp at a time until frosting reaches desired consistency.

Frost cupcakes and garnish with candied lemon peel (optional).