Mix cornstarch and water in a small bowl until dissolved. Warm strawberries and sugar in a saucepan over medium heat, stirring and breaking up some strawberries. Bring to a simmer and stir in the cornstarch mixture. Simmer for 5 minutes, then remove from heat and stir in lemon zest. Cool completely.

Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners.

In a large bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.

In a medium bowl, whisk melted butter and sugar together. Add egg whites, sour cream, milk, and vanilla bean paste/extract. Mix until combined.

Pour wet ingredients into dry ingredients and whisk until batter is combined.

Fill cupcake liners 2/3 full with batter and bake for 20-22 minutes or until a toothpick comes out clean.

Allow cupcakes to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Cut a pocket into the center of the cooled cupcakes to create a well. Spoon in the cooled strawberry filling.

Whip heavy cream, sugar, and vanilla bean paste/extract on medium-high speed until medium peaks form. Fold in reserved strawberry filling.

Frost cooled cupcakes with whipped cream and garnish with sliced strawberries and fresh mint.

Serve immediately or refrigerate until ready to serve. Store leftover cupcakes in the refrigerator for up to 5 days.