1. Preheat oven to 350°F.
2. Grease and flour an 18 x 13-inch sheet pan and set aside.
3. Combine butter and sugar in a large bowl and beat with an electric mixer until creamy. Add eggs one at a time, mixing well after each egg. Stir in vanilla and mix well.
4. In a separate bowl, whisk together flour, baking powder, and salt. With the mixer on low-speed, alternate adding flour and milk to the butter mixture until ingredients are completely combined.
5. Pour batter into prepared pan and bake for 15 to 17 minutes. Allow cake to cool completely.
6. Cut the cake in half and spread the lemon curd onto the bottom half of the cake.
7. Place the top of the cake back on the cake with the lemon curd filling and cut into 2" squares.
8. Melt the candy melts in the microwave in 30-second increments until the wafers have completely melted. Pour the melted candy over cakes and allow to cool completely.
9. Top with Valentine heart candies if desired.

Lemon Curd:

1. Whisk together lemon juice, lemon zest, sugar, and eggs in a heavy saucepan.
2. Stir in butter and cook over low heat, whisking frequently until curd is thick and bubbles appear on surface.
3. Transfer curd to a bowl, cover with plastic wrap and chill for about 1 hour.

Recipe Notes: You can make the lemon curd up to 3 days ahead.