Preheat the oven to 350 degrees F and line 12 muffin tins with paper liners. 

In a large bowl, whisk together the milk, vegetable oil, eggs, and vanilla. 

Next, add the sugar and whisk to combine. 

Finally, add the flour and baking powder. Whisk just until combined— you don’t want to overmix! 

Divide the batter between the muffin tins, filling each one with ¼ cup of batter. 

Bake for 16-18 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. 

Remove the cupcakes to a wire rack and allow them to cool completely before frosting. 

Add all of the ingredients, raspberries, blueberries, strawberries, lemon juice, and cornstarch, to a small saucepan set over medium heat. 

Cook, stirring often, for 5-7 minutes or until the berries have broken down and the sauce has thickened. 

Remove the pan from the heat and allow it to cool completely before filling the cupcakes. 

Add the softened butter and mascarpone to the bowl of a stand mixer fitted with the paddle attachment. Beat on medium speed until well combined, about 1 minute. 

Turn the mixer to low speed and slowly add the powdered sugar. When all of the powdered sugar has been incorporated, add the vanilla. 

Turn the mixer to medium speed and beat until the frosting is light and fluffy, about 2 minutes. 

Transfer the frosting to a piping bag fitted with your choice of tip. I’m using a Wilton 2D. 

To assemble the cupcakes, cut a small hole from the center of each cupcake, about the size of a quarter and ¼ inch deep. 

Fill the hole with 1-2 teaspoons of berry filling and then place the cutout piece of cake back on top. 

Pipe the vanilla mascarpone frosting on top of each cupcake and garnish with a fresh berry and/or sprinkles, if desired. 

Storage: Store leftover cupcakes in an airtight container in the fridge for up to two days.