Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or three 8-inch round cake pans.
Step 2: In a large bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt.
Step 3: In a separate medium bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract.
Step 4: Pour the wet ingredients into the dry ingredients and mix on low speed until just combined. Gradually add the hot water (or coffee) and mix until the batter is smooth. The batter will be thin, which is normal.
Step 5: Divide the batter evenly among the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. Let the cakes cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely.
Step 6: While the cakes cool, prepare the frosting. In a large bowl, beat the softened butter with an electric mixer until light and fluffy (about 2-3 minutes).
Step 7: Gradually add the powdered sugar, one cup at a time, beating well after each addition. Pour in the heavy cream, vanilla extract, and pinch of salt. Beat on high speed until the frosting is light, fluffy, and smooth. If the frosting is too thick, add more cream one tablespoon at a time; if too thin, add more powdered sugar.
Step 8: To assemble the cake, place one cooled cake layer on a serving plate or cake stand. Spread a generous layer of frosting over the top. Arrange a layer of sliced strawberries over the frosting.
Step 9: Place the second cake layer on top, spread with more frosting, and add another layer of strawberries. If using a third layer, repeat this step.
Step 10: Place the final cake layer on top. Use the remaining frosting to frost the top and sides of the cake smoothly or decoratively. Garnish with fresh whole or sliced strawberries just before serving.