In a large mixing bowl, combine a box of vanilla cake mix with the ingredients as listed on the box. Add 1/2 teaspoon vanilla extract and 1/2 cup light sour and beat until all ingredients are well combined.
Line two 12-cavity muffins pans with liners. Divide the cupcake batter evenly between each liner.
Bake the cupcakes at 350°F for 15-18 minutes. Check the cupcakes for doneness by inserting a toothpick into the center of the cupcake. If the toothpick comes out clean, then your cupcakes are done.
Allow the cupcakes to cool in the pan for 10-15 minutes and then transfer to a wire rack and cool completely.
Once cooled, hollow out the center of each cupcake with the cupcake corer or a knife about halfway down through the cupcake.
Use a knife or spoon to fill the center of each cupcake with 1-2 teaspoons of the strawberry jam.
For the Frosting:
Soften butter in the microwave for 10 seconds then flip the butter over to the opposite side. Microwave again for 5 seconds.
In a large mixing bowl, whip the butter for 3-4 minutes until the butter is fluffy and well whipped.
Slowly add the powdered sugar 2 cups at a time. I suggest reducing the mixer speed so the powdered sugar does not fly everywhere. Once incorporated, increase the mixing speed to medium-high and beat for 30 seconds.
As you are adding the powdered sugar, the frosting will become thick and crumbly. Alternate adding the heavy whipping cream, strawberry jam and vanilla extract in between the cups of powdered sugar. Toss in the pinch of salt last.
Once all of the ingredients have been added, beat at a high speed for 60 seconds so the frosting becomes is nice and light.
Chop 4 of the pop tarts into small pieces, about the size of a quarter. Toss the pop tarts into the mixer and beat into the frosting for 30 to 60 seconds until well incorporated.
Use a large cookie scoop (about 3 tablespoons size) and scoop the frosting onto the top of the cupcakes. Tap the cupcake on the counter a couple of times to adhere the frosting to the top of the cupcake.
Cut remaining 4 pop tarts into triangles to place on top of the cupcakes before serving.
Keep the cupcakes covered in an airtight container until serving.