Put an oven rack in the middle of the oven and preheat to 350 degrees F. Line a standard 12 cup muffin tin with cupcake liners.
In the bowl of a stand mixer, add the butter and sugar and beat until light and fluffy, about 3 to 4 minutes.
Meanwhile, in a medium bowl, whisk together the flour, baking powder, and salt.
Add the sour cream to the butter and sugar mixture and continue to beat until incorporated. Add the eggs and yolk, 1 at a time, beating until thoroughly mixed into the batter. Add in the vanilla and continue to mix. Slowly add the dry ingredients, in increments, and mix until combined.
Scoop the batter into the cupcake liners to fill 3/4 of the way. Put in the oven and bake until the cupcakes are a pale gold color and a cake tester comes out clean, about for 18 to 20 minutes. Remove the cupcakes from the oven and let cool in the tins for 5 minutes. Remove to a wire rack to cool completely before frosting and filling.
Meanwhile, fit a plain pastry tip to the bottom of a gallon-sized resealable plastic bag and fill with strawberry jelly. Once the cupcakes are cool, insert the tip far into the cupcake and slowly squeeze in about 1 tablespoon or so of jam. Be careful not to overfill the cupcakes or they will crumble and explode. Repeat with the remaining cupcakes. Frost the cupcakes with the Peanut Butter Cream Cheese Frosting using a pastry bag and a star tip. Sprinkle lightly with the confetti sprinkles and serve.
Peanut Butter Cream Cheese Frosting:
In a large bowl, add the cream cheese and butter. Beat until well combined, then add the vanilla and peanut butter and beat until well mixed. Slowly add the confectioners' sugar and beat until well incorporated.