Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.

In a large bowl, cream together the softened ½ cup butter and 1 cup granulated sugar with an electric mixer until light and fluffy, about 2-3 minutes.

Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract.

Add the ½ cup creamy peanut butter to the butter mixture and beat until well combined and smooth.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Begin and end with the dry ingredients (add ⅓ of the dry, then ½ of the milk, another ⅓ of the dry, the remaining ½ of the milk, and finish with the last ⅓ of the dry). Mix on low speed until just combined, being careful not to overmix.

For each cupcake wrapper, add about 1 tablespoon of batter. Then, carefully spoon about ½ teaspoon of jelly or jam into the center of each batter-filled cup.

Spoon the remaining batter over the jelly, ensuring the jelly is fully covered. Fill each cupcake liner about two-thirds full. You can gently swirl a toothpick around in the center to create a little vortex if you like, but it's not essential.

Bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.

Let the cupcakes cool in the muffin tin for 5-10 minutes before transferring them to a wire rack to cool completely before frosting.

While the cupcakes are cooling, make the frosting. In a medium bowl, beat the softened ½ cup butter and ⅓ cup peanut butter with an electric mixer until smooth and creamy.

Gradually add the powdered sugar, mixing on low speed until combined. Add 2 tablespoons of milk and the vanilla extract, and beat until the frosting is light and fluffy. Add the remaining tablespoon of milk if needed for a smoother consistency.

Once the cupcakes are completely cool, generously frost each one with the peanut butter frosting. You can use a piping bag with your favorite tip for a decorative touch or simply spread it on with a spatula.

Gently drizzle or spoon about ½ teaspoon of jelly on top of the frosted cupcakes. You can use a toothpick to swirl it slightly into the frosting for a pretty marbled effect if desired.