Preheat your oven to 350°F (175°C). Prepare the half sheet pan by greasing it and lining it with parchment paper. Don’t forget to grease the parchment paper too.

In a mixing bowl, whisk together the flour, baking powder, and salt until combined.

In a separate bowl, use an electric mixer to beat the unsalted butter and sugar together until fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla until combined.

Alternate adding the dry ingredients and buttermilk into the butter mixture until fully incorporated.

Spread the batter evenly into the prepared pan and bake for 15 to 20 minutes until the edges are lightly golden brown.

Cool the cake in the pan for about 10 minutes, then transfer it to the fridge to chill for about 20 minutes.

In the meantime, make the filling by beating the unsalted butter and marshmallow fluff together until smooth.

Add the confectioner's sugar and vanilla extract to the butter mixture and mix until combined and fluffy.

Once the cake has cooled, cut out hearts using a 4-inch heart-shaped cookie cutter. You will need two hearts for each cake.

Pipe the filling onto half of the heart-shaped cakes and place the remaining hearts on top to create a sandwich.

Freeze the assembled cakes for 1 hour to set the filling.

Melt the candy melts in a microwave-safe bowl with the coconut oil. Stir until smooth.

Dip each frozen cake into the melted candy mixture, covering it completely.

Place the dipped cakes on a baking sheet lined with parchment paper and let them set in the refrigerator for 15 minutes.

Finally, pipe melted white chocolate into swirls on top of each cake for a beautiful finish and chill them again to let the swirls set.