Preheat the oven to 350°F. Line a muffin tin with cupcake liners.
Beat the butter and sugar together until light and fluffy. Add in the peanut butter and the eggs and beat until fully incorporated. Mix in the vanilla.
In a separate bowl, mix together the flour, salt, baking powder, and baking soda. Mix well.
Alternate adding the flour in three additions and the milk in two additions. Mix each addition in until just combined.
Evenly divide the batter among the cupcake liners and bake for 15-18 minutes, or until a toothpick comes out clean.
Allow to cool completely and cut out the centers of the cupcakes. Add in the jam into the center. Take the parts you’ve cut out and remove the inside section and replace the tops of the cupcakes back onto the cupcakes.
To make the frosting, beat the butter until creamy. Add in the powdered sugar one cup at a time, beating well between each addition. The mixture will end up looking crumbly and lumpy, this is normal.
Add in the jam and salt and beat well. Stir in the vanilla and lemon zest.
Add in the heavy cream as needed to achieve the consistency you desire.
Fill a piping bag with the frosting and pipe the frosting onto the cupcakes.
Serve immediately, or within three days.
Keep a careful eye on the cupcakes as they can dry out easily in the oven