To make cake topper, outline a template of a small heart shape on a parchment paper.
Place candy melts in a microwaveable Ziploc bag. Microwave on high for 20 to 30 seconds to completely melt the candy melts. Add oil if it’s too thick to pipe. Push the melted candy toward one corner of the bag. With a pair of scissors, snip off a very small opening.
Start piping the candy over the template, starting with the outline. Place a toothpick in the middle, then fill the outline with zigzags.
Let it dry completely before peeling the cake topper off the parchment paper.
Preheat oven to 325F. Grease three 5-inch cake pans and line bottoms with parchment paper. Set aside.
In a standing mixer with a whisk attachment, whisk eggs and sugar on high speed for 5 minutes, until light and triple in volume.
Mix in vanilla, lemon juice and zest.
In a large bowl, sift together the flour and salt.
Add the flour mixture to the egg mixture on low speed, and mix until just incorporated.
Spoon about 1/2 cup of the cake batter into a bowl, and stir in the melted butter. Add the mixture back to the cake batter and gently fold with a spatula until blended.
Pour the batter into the prepared pans evenly and smooth the top. Bake for about 20 minutes, until the centre of the cakes spring back when gently pressed. Let cool completely in the pans.
Run a pairing knife around the edge of the cake to loosen it from the pan. Peel off the parchment paper circles.
To prepare buttercream, beat butter for a few minutes in a standing mixer with the paddle attachment on medium speed. Add powdered sugar and turn your mixer on low, beat until the sugar incorporates with the butter. Add heavy cream, lemon zest and juice, beat on medium speed for another 3 minutes, or until buttercream becomes light and fluffy. Add food coloring, if you prefer, and mix for another minute.
To assemble the cake, sandwich each cake layer with a thick layer of buttercream. Top with a final layer of buttercream. Use an offset spatula to smear the buttercream squeezed out between the cake layers along the sides of the cake to create the naked cake effect.