First make the caramel sauce and let it cool.

For the Vanilla Cupcakes

• Preheat the oven to 350 and line 2 cupcake pans with a total of 15 liners, spreading them out in the pan.
• In the bowl of a stand mixer, whisk together the flour, cornstarch, sugar, baking powder, baking soda, and salt.
• Cube the butter, then add it and the vegetable oil to the dry ingredients and mix using the paddle attachment on medium speed. Stop once the mixture resembles wet sand.
• In a separate bowl or large liquid measuring cup, whisk the water and sour cream until smooth. Then, add the vinegar, eggs, egg yolk, and vanilla extract and whisk until smooth.
• With the mixer running on low speed, slowly stream in the sour cream mixture until combined.
• Do a final mix by hand to ensure the batter is mixed evenly.
• Fill the cupcake liners half full, then bake at 350 for 15-16 minutes, or until a toothpick comes out mostly clean with a few moist crumbs attached. Let the cupcakes cool completely.

For the Salted Caramel Cream Cheese Buttercream

• In the bowl of a stand mixer with the paddle attachment, cream the butter and cream cheese for 10 minutes. Stop the mixer every couple of minutes to scrape down the bottom and sides of the bowl.
• Once the butter/cream cheese mixture is completely smooth add half of the powdered sugar (2 C) and mix on the lowest speed for 3 minutes.
• Scrape down the bowl again, then add the remaining powdered sugar and again mix on low for 3 minutes.
• Add the salted caramel sauce and mix to combine. The caramel should be room temperature or slightly warm, but NOT hot when you add it to the frosting.

Assemble

• Use a pairing knife to hollow out a small hole in each cupcakes – aim for about 1/2″ wide and deep. Discard the extra cake, or have a nice little chef snack.
• Fill the cupcakes with the caramel sauce. You can do this with a spoon, or I find using a piping bag is super easy and mess free.
• To swirl extra salted caramel into the buttercream while piping you’ll have to prepare your piping bag in a certain way –
  • Cut off the tip of the piping bag and insert your favorite tip – I used a Wilton 8B here. Then, use a butter knife or a long skinny spatula to create a line of salted caramel along the seam of the bag starting all the way inside the tip, and up about 4″ from the top of the bag.
  • Then, fill the bag with the buttercream, again stopping about 4″ from the top of the bag.
  • Twist the bag closed then pipe swirls on top of each cupcake.