Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners.

In a medium bowl, whisk together the flour, baking powder, and salt until well combined.

In a large mixing bowl, use an electric mixer to cream the butter and sugar until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.

Gently fold in the mixed berries with a spatula, being careful not to overmix.

Divide the batter evenly among the cupcake liners, filling each about two-thirds full. Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cupcakes to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

In a large bowl, beat the softened butter until creamy. Gradually add powdered sugar, beating well after each addition. Stir in the vanilla extract and heavy cream, beating until the frosting is light and fluffy.

Using a piping bag fitted with a star tip, swirl the frosting onto the cooled cupcakes. Top each with a few fresh berries for garnish.

Serve the cupcakes at room temperature, pairing them with a cup of tea or coffee for a delightful experience.

Store unfrosted cupcakes in an airtight container at room temperature for up to three days. For longer storage, freeze the cupcakes for up to a month, then thaw and frost them before serving.