Start by mixing the melted butter with the condensed milk and set it aside.
In a stand mixer bowl combine the eggs, sugar, salt and whip it until light and fluffy on a high speed for about 5-7 minutes.
Sift in the flour, cornstarch and baking powder. Mix all together using a spatula. Add the mix of butter and condensed milk and mix again.
Pour the cake batter on a baking sheet covered with parchment paper. I use a half sheet pan which is 18 by 13 inches. Spread the cake batter evenly with a spatula and bake at 350 F degrees for 15 to 18 minutes or until the skewer inserted into the cake comes out dry. Very important not to overbake the cake or it will turn out dry. Transfer the cake onto a cooling rack and let it cool completely.
In a large mixing bowl combine the sour cream, powdered sugar, vanilla extract and mix it using a hand mixer. Add the condensed milk and mix again. That’s it, our filing is ready.
I will assemble the cake in a mixing bowl, which I lined with plastic wrap on the inside. The top diameter of my bowl is 8 inches. I will also need a plate that is a little bit smaller than the diameter of the bowl.
When the cake has cooled down, place the prepared plate in the middle and using a sharp knife cut out the circle. It will be the bottom of our future cake. Cut the rest of the cake into 1-inch cubes.
To assemble the cake, spread a little bit of cake filling on the bottom of the bowl. Deep the cake cubes into the cake filling and lay out a single layer on the bottom of the bowl. Next, spread the walnuts and chunks of pineapple. Repeat the process until the bowl is full. I got three layers of cake cubes, walnuts and pineapples.
Spread the rest of the filling on top of pineapples and cover with the round cake layer. If you prefer a very moist cake, soak this cake layer with pineapple juice from the cane. Cover the bowl with a plastic wrap and refrigerate for 6 to 8 hours or overnight.
Bring a saucepan with a few inches of water to a simmer, reduce the heat to medium low and place the bowl on top. Combine the egg whites with sugar and using a hand mixer start whisking the mixture on the lowest speed of your mixer until the sugar has dissolved, the mixture has increased in volume and turned slightly white. This should take about 8-10 minutes. You can rub a bit of the meringue between your fingers to make sure there are no undissolved sugar crystals left.
Take the bowl off the saucepan and wipe the bottom of the bowl with a towel. Next, we need to bring the meringue to room temperature. I will transfer the meringue to a clean mixing bowl and keep whisking until it cools down. At this point, you can also transfer the meringue into a stand mixer bowl and let the mixer do the work for you.
When the meringue gets to room temperature, add room-temperature butter one tablespoon at a time, mixing after each addition. Add vanilla extract or any other flavor, if using, when the buttercream is almost ready. Beat until the butter is combined and the mixture has reached a silky consistency.
Take the cake out of the refrigerator, take off the plastic wrap and invert the bowl onto a cake board or a serving plate. Carefully remove the mixing bowl and the plastic wrap around the cake.
Now we’re ready to decorate the cake. I will decorate my cake with light pink to a dark purple tulip. Using pink gel food coloring, I colored about a cup of the buttercream. Before transferring the buttercream into a piping bag fitted with an extra-large tulip piping tip, I like to take a brush and apply some pink food coloring inside the pastry bag. It’s a great way to add more visual color without adding to much food coloring into the frosting. To pipe tulips, hold the piping bag just above the surface, squeeze and the buttercream will come down to make contact with the cake. Finish by pulling up without squeezing.
Using the same mixing bowl, I colored the next batch of buttercream into a light purple color and filled the same piping bag on top of my pink buttercream. I keep piping the tulips gradually changing to a darker color.
When all the tulips are piped, using green buttercream pipe leaves to fill in the blank spaces between the flowers. When all the leaves are piped, I use a small round piping tip and I fill in the little empty spaces.