The first thing we need to do is to preheat the oven to 350ºF and prepare the pans we are going to use. We need either 2 9 inch cake pans or, if you wanted the more traditional look, 1 9 inch pan, 1 6 inch pan and 1 3 inch pan. This way, the cake will taper towards the top, looking like a small castle.
To prepare them, butter and flour them so that it is easier to take the cake out once they are done. You could also line them with parchment paper if you prefer.
Now to make the cake. Grab the room temperature butter and place it in a large mixing bowl with the sugar. With the help of a stand or hand mixer, cream it until fluffy on high speed with a paddle attachment. This will take approximately 5 minutes.
Reduce the speed to medium and proceed to add the eggs in batches. We recommend no more than 2 at a time. Then mix thoroughly.
Add in the sour cream, the vanilla extract, and the lemon zest.
Sift together the flour, cornstarch, salt, and baking soda together to avoid any lumps and have an even mix.
Add in the dry ingredients slowly, making sure there is no powder splash. Continue to mix after you have incorporated all of it. You will know it is done once you scrape the sides and can tell there are no butter or flour pockets in it.
Once your batter is ready, you will need to divide it proportionately into the cake pans. If you have a scale, this will be much easier, but one way to get the measurements right with weighting is the following.
You can, first, divide the batter into two equal parts. One of these you will need to pour into the 9-inch cake mold. Remember they need to be buttered and floured or have some sort of parchment paper lining.
You will be left with half the batter. You must then divide this into 3 equal parts. Use one of these for the 3-inch cake pan and the other 2 for the 6-inch cake pan. See? Very easy!
Smoothe the tops of the batter with a spatula before baking. This will help so that there is not so much of a round top to be cut off the cakes before stacking them.
As you could have imagined, they will need different baking times as the pans are different sizes. The 9-inch will take approximately 45 minutes to be done. The 6-inch, 35 to 40 and the 3-inch 30 minutes.
Always check them a little bit before they are due and only take them out once a stick or knife comes out clean from the center.
Cool the pans to room temperature before unmolding them and then let them rest top sides down on a cooling rack until they are completely cool. You could even, if you have enough space, place them in the fridge. This will make it easier to frost them, cut them and stack them.
Now let’s move on to the frosting. Go back to your electric or hand mixer and cream the butter for a few minutes.
Once it is light and fluffy in texture, sift in the powdered sugar slowly while still mixing on low. Also, add the vanilla extract.
Check the consistency. If it is too stiff, add in milk slowly to adjust it and make it just right. This depends on the temperature and humidity of your kitchen, so the quantities are just estimates.
Set aside a quarter of the frosting and add food coloring as you desire. For a traditional look, we recommend you further divide this into 3 and use a bit of yellow, blue and red to make pastel colors.
Once everything is done and the cakes are cool, check to see if their tops are level. If they are not, you will need to adjust them with a serrated knife before stacking them.
Cut them into halves and place buttercream between them. Then stack them all together. You can chill the cake for a few hours at this point.
Crumb coat the cake with a thin layer of frosting before proceeding to actually frost it. This will help the buttercream stay smooth and look amazing. Then pipe in some decorations as you see fit.