Preheat the oven to 350F and line a cupcake tin with 12 paper liners. Then add 2 more liners to a loaf pan or any small baking pan (these two extra cupcakes will be used for decoration).

In a large bowl using a hand or stand mixer with the paddle attachment, mix together the butter, oil, and sugar until creamy and fluffy, about 1 minute. Then mix in ½ cup (150g) of the sweetened condensed milk (set the rest off to the side for the frosting) and vanilla flavor until fluid and well blended.

Then mix in the eggs, followed by the sour cream. Now add in the cornstarch, baking powder, and salt and mix until blended. Then mix in the flour just until you reach a smooth and creamy batter. Careful not to overmix. Use a spatula to fold in the sprinkles by hand.

Divide the batter evenly between the 14 liners, filling each about ¾ full. Bake for 22 to 25 minutes or until evenly puffed and a toothpick inserted comes out clean with a few moist crumbs. It’s ok if the two extra cupcakes spilled out of the liners. We’ll be crumbling them up anyway!

Allow the cupcakes to cool in the pan for about 5 minutes, then transfer to a cooling rack to cool completely before making the frosting. In the meantime, finely crumble the extra 2 cupcakes onto a plate and toss with a couple extra tablespoons of sprinkles.

In a large bowl using a hand or stand mixer with the paddle attachment, mix the butter and salt on medium high speed until smooth and creamy, about 1 minute. Then mix in the powdered sugar one cup at a time on medium speed. Scrape down the bowl between each cup. Then mix in the vanilla.

Once the frosting is smooth, slowly mix in the remaining sweetened condensed milk, adding it in three additions. Wait until each addition is fully incorporated before adding the next. Stir in the final addition by hand.

Add the frosting to a piping bag and top each cupcake with a swirl. Use your hand to scoop and press the cupcake crumbles around the sides. Now they’re ready to enjoy!

To store, keep the cupcakes in a container in the refrigerator. They also taste really good chilled, and the frosting turns into a delicious fudgy consistency!