1. Preheat your oven to 360°F.
2. Line the bottom of two cake pans with parchment paper, or spray well with non-stick baking spray.
3. Sift Yellow Cake Mix into a large bowl. Add eggs, oil, vanilla, and milk. Mix well until a batter forms.
4. Pour batter evenly into two, heart-shaped cake pans. Cool completely in the refrigerator or freezer.
5. Make the frosting. With a stand mixer or hand mixer, beat the coconut oil until light, fluffy, and smooth. Continue to beat. Slowly add half of the confectioners sugar, vanilla, and half of the milk. Slowly add the rest of the confectioners sugar, and then the remainder of the milk.
6. Beat the frosting until completely smooth and lump-free.
7. Assemble the cake. Once the cakes are completely cooled, carefully remove them from the cake pan.
8. Lay one of the cake hearts on your work surface and spread half of the frosting evenly across the top.
9. Carefully place the second cake heart upside down on top of the frosted cake heart. Using the remainder of the frosting, lightly coat the top and sides of the cake.
10. Dust a clean work surface with cornstarch or confectioners sugar.
11. Knead the fondant until it's soft and pliable. If you're going to add color to it, do so now. Set aside a small amount of fondant to use when adding decoration.
12. Roll the rest of the fondant 1/8" thick. Carefully lift it from your work surface and place it on top of the cake. Use your hands to mold it to the shape of the cake. Trim the excess with a sharp knife.
13. If making decorations for the top of the cake, knead a small amount of food coloring into the fondant and roll 1/8" thick. Cut out heart shapes with cookie cutters or a sharp knife, and secure the decorations to the cake with a small brush of water. Enjoy!