• Preheat the oven to 350 degrees F and line a muffin tin with cupcake liners.

Make the Cupcake Batter:

• In a medium mixing bowl, whisk together the flour, baking powder and salt. Set aside for now.
• In the bowl to the stand mixer, beat on high the butter with the sugar until smooth, about 2 minutes
• Add the eggs and vanilla extract and beat on high until just incorporated. About 1 minute.
• Add 1/3 of the flour mixture to the bowl and beat on medium until mixed in.
• Add 1/2 of the milk to the bowl and beat in. Continue adding the flour mixture and milk alternately ending with the flour, beating between addition.

Bake the Cupcakes:

• Divide the batter between each muffin cavity filling about 3/4 full. Bake for 18 to 20 minutes or until an inserted toothpick comes out clean and the cupcake bounces back when pressed.
• Cool in the pan for 5 minutes before transferring to a cooling rack to cool completely.

Make the Lemon Curd:

• In the meantime, let’s make the lemon curd. Whisk together the eggs yolks, sugar, lemon zest, lemon juice, salt in a medium saucepan. Heat on low, whisking constantly, until the mixture starts to become thick, 10 to 12 minutes. Whisking keeps the eggs from “scrambling” and curdling so it is vital for this step.
• Remove from heat and whisk the butter in immediately.
• Pour into a small mixing bowl and cover immediately with plastic wrap. The plastic will keep a skin from developing on the curd. Set aside to cool completely. The curd will continue to thicken and the plastic will peel off when cooled.

Make the Lemon Frosting:

• Once everything has cooled, start making the buttercream frosting. In the bowl to your stand mixer, beat the butter on high until smooth.
• Add 1 and 1/4 cups of the powdered sugar and the lemon juice and beat until smooth. Add the remaining powdered sugar and beat until smooth. Transfer to a piping bag.

Assemble the Lemon Stuffed Cupcakes:

• Use a small knife or the tip of a piping bag to hollow out the middle of the cupcake.
• Pipe the frosting around the edges of the hollowed out middle. The frosting will act as a barrier and provide a decorative edge.
• Fill the hollowed out cavity with lemon curd to the edge of the icing. Chill for 15 to 20 minutes before enjoying.