For cake: Preheat oven to 325°F. Grease 2 8-inch cake pans with butter, and line with parchment paper rounds. Dust pans with flour.
Combine flour, sugar, cocoa powder, baking soda, baking powder and salt together in the bowl of a stand mixer fitted with a paddle attachment. Mix on low speed until combined.
Whisk buttermilk, water, oil, eggs, and vanilla together in a separate large bowl. With the mixer on a low speed, slowly add buttermilk mixture into flour mixture until just combined, scraping down sides and bottom of bowl as needed.
Divide batter between prepared pans. Bake until a toothpick inserted into the center comes out clean, about 30-35 minutes. Let cakes cool in pans for 10 minutes. Invert onto wire racks and let cool completely
For buttercream and assembly: Meanwhile, beat butter in the bowl of a stand mixer fitted with a paddle attachment until light and fluffy, about 2 minutes. With mixer on low, gradually add powdered sugar, followed by heavy cream, vanilla and salt.
Once ingredients are combined, turn mixer to medium-high and beat for about 3-5 minutes. Scrape down sides of the bowl and beat 2 more minutes.
Once cakes have cooled, create a flat cake surface by removing a 1/4-inch from the crown of the cake with cake level. Stack layers together and make two cuts to create a pointed bottom end (cuts will be about 1.5-2-inches deep at most). Move cut ends to the top of the cake to create a heart shaped cake.
Transfer one layer to a 10-inch cake drum. Place on cake turntable. Using an offset or straight spatula, spread roughly 1/2 to 1 cup of buttercream evenly over the top, right to the edge of the cake. Press roughly 1 cup strawberries into frosting. Place second cake layer on top, pressing gently to adhere. Repeat with the remaining third cake layer and strawberries, finishing with the fourth layer of cake. Refrigerate for at least 30 minutes, until buttercream is set.
Divide remaining buttercream into 4 separate small bowls. Leave one bowl white. Add red, pink, and lavender gel food coloring individually to each bowl, adjusting shades as desired.
Transfer colored buttercreams into 4 different piping bags fitted with coupler attachments and tip K47, K38, K21, K02. Pipe rosettes and stars, as desired, all over the top of the cake. Transfer back to the refrigerator for at least 30 minutes, until buttercream is set. Slice and serve.
