How to Bake and Stack a Two Tier Cake

Preheat your oven to 350° F and spray 3 8 inch round cake pans and 3 6" round cake pans with baking spray or line with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl- combine eggs, yolk, oil, and sugars and mix well until combined.
Combine the flour, baking soda and salt in a bowl and slowly add to the mixture on low speed.
Slowly add in milk, and vanilla and continue mixing until a smooth batter forms, about 1-2 minutes.
Evenly pour the batter into the pans and bake for 28-30 mins for the 6" and 35- 40 mins for the 8" The cake is done when a toothpick is inserted and comes out clean and when the edges are pulling away from the sides and are golden brown.

Using the cake leveler or a long serrated knife, level off the cakes so they have a flat top.
Place a 10" cake board on the turntable, and a dab 1 tsp of buttercream in the middle and smooth it out. Place the 8" cake board on top and press it to stick to the 10" board. Smooth 1 tbsp buttercream on top of the 8" cake board, then place your first 8" cake layer on top.
Using either a piping bag with a round tip or an offset spatula, place down 1/4 cup of buttercream on top of the cake, starting in the middle and smoothing to the outside. Leave 1/2" from the sides so it doesn't overflow over the cake. If using a piping bag, pipe a border around the cake and then fill the middle.
Take the next 8" cake layer and turn it upside down so that the bottom is now the top. Place it on top of the filling. The cut side down should be on top of the buttercream. Repeat the process of filling the cake layer with buttercream and topping it with the last 8" cake layer.
Using the offset spatula, and the turntable frost the entire cake (spinning as you go) from bottom to top for a light crumb coat. Place in the freezer for 15 minutes to seal in the crumbs.

Repeat the same steps as above for filling and frosting the 6" layer. Start by spreading 1/2 tbsp frosting over the 6" cake board and end by putting the cake in the freezer for 15 minutes. You should now have 1, 8" cake layer, and 1, 6" cake layer

Using the offset spatula again, frost both of the entire cakes using more buttercream this time. When the cake is mostly covered with buttercream, switch to the bench scraper and smooth out the sides and tops of the cakes. Don't worry if it isn't perfect.
Fill your water bottle with clean water and lightly spray one cake at a time on the turn table. Using the bench scraper again, smooth out any cracks. Repeat for the second cake.

Using bubble tea straws or wooden dowels place 4 straws in a square shape in the center of the 8" cake making sure that they are being placed under where the 6" cake will be. Push each straw into the cake, then mark the straw where it hits flush with the cake and cut off the rest of the straw. The straws should be the same height as the 8" cake or a little under, just not higher.
Spread a thin layer of buttercream over the straws.
Using the offset spatula, lift the bottom of the 6" cake and hold it with 2 hands from the bottom. Center it above the 8"cake, get as close as you can and drop it into place on top of the 8" cake and straws.
Continue decorating as you please! YOU DID IT!