Preheat oven to 350F. Grease three 5-inch cake pans and line bottoms with parchment paper. Set aside.
To prepare the vanilla cake, sift flour, baking powder, baking soda and salt in a large bowl.
In another bowl, mix eggs and sugar until well combined. Gradually add oil and vanilla, mix until just blended.
Slowly add half the flour mixture; mix until just blended. Add the buttermilk, mix until just blended. Add remaining flour mixture, mix until batter is combined and smooth.
Pour the batter into the prepared pans evenly and smooth the top. Bake for about 20 minutes, until a toothpick inserted in the centre comes out clean.
Remove the cakes from the oven and place on a wire rack to cool for about 10 minutes. Remove the cake from the pan and cool completely.
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 vanilla and heavy cream, beat on medium speed for another 3 minutes, or until buttercream becomes light and fluffy.
Tint 1/4 cup buttercream with the red coloring paste to create deep red color. Transfer to a piping bag fitted with a tiny round tip. Set aside.
To make the heart inside the cake, trim to level the top of the cake layers. Reserve the cake scraps.
Centre a 3-inch round cookie cutter on top of one cake layer and gently press a circle as a guideline. Cut a small inverted V on the guideline by inserting a knife into the cake at a 45-degree angle just half inch outside the guideline and make a cut along the whole cake. Finish the V by inserting the knife at a 45-degree angle half inch on the other side of the guideline, meeting the other cut, and cutting around the cake.
Remove the excess cake from the V and save it with the other scraps. Reserve 1/4 cake scraps.
To make a red cake mixture, combine the remaining cake scraps with a tablespoon of red buttercream. Mix until it is fully incorporated and pliable. Roll out a long skinny triangular. Carefully fit the triangular into the V channel. If it breaks, gently press it back together.
Gently run a knife down the centre of the triangular. This will be the indentation at the top of the heart. Fill the indentation with the reserved plain cake scraps.
To assemble the cake, place a cake layer on your serving plate and spread a thin layer of white buttercream on top. Place the cake layer with a heart on top with another thin layer of white buttercream. Top it with the remaining cake layer. Frost the cake top and sides with the white buttercream. Chill for 30 minutes.
Use the red buttercream to pipe MOM I HEART YOU! along the bottom of the cake. Go around the cake and keep piping over and over again.