Prep your pan and oven: Line a 12-cup muffin pan with paper liners. Preheat the oven to 350°F (175°C).
Mix the dry ingredients: In a bowl, whisk together flour, baking powder, baking soda, and salt.
Set aside.
Cream butter and sugar: In a large bowl, beat the butter and sugar until light and fluffy, about 2–3 minutes. This step builds a tender crumb.
Add eggs and vanilla: Beat in the eggs one at a time, then mix in the vanilla. Scrape the bowl so everything blends evenly.
Combine wet and dry: Stir the sour cream and milk together.
Add the dry ingredients to the butter mixture in two additions, alternating with the milk mixture. Mix on low just until combined. Do not overmix.
Fill and bake: Divide the batter evenly among the liners, filling each about two-thirds full.
Bake 16–19 minutes, or until a toothpick comes out clean. Cool in the pan 5 minutes, then transfer to a rack to cool completely.
Make the strawberry filling: In a small bowl, toss diced strawberries with sugar and lemon juice. If you want a thicker filling, sprinkle in cornstarch and let the mixture sit 10–15 minutes to lightly thicken.
Whip the cream: In a chilled bowl, beat heavy cream, powdered sugar, vanilla, and a pinch of salt to medium-stiff peaks.
Keep cold until ready to use.
Core the cupcakes: Once cupcakes are cool, use a paring knife or cupcake corer to remove a small plug from the center of each, leaving a 1/2-inch border.
Fill with strawberries: Spoon about a tablespoon of the strawberry mixture into each cavity. Replace a small portion of the cupcake plug on top to keep the filling in.
Top with whipped cream: Pipe or spoon a generous swirl of whipped cream over each cupcake. Garnish with a strawberry slice and mint if using.
Serve: Enjoy right away for the best texture and flavor.