Preheat oven to 350°F. Line three 8" pans with parchment rounds, and grease with non-stick baking spray.

Mix together 3 cups all purpose flour, 3 cups sugar, 2 1/2 tsp baking powder and 1 tsp salt in a stand mixer with a paddle attachment or hand mixer until fully combined.

Mix in 1 cup of unsalted butter slowly into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain and the mixture looks crumbly.

Pour in 1 cup of egg whites and mix on low until just incorporated. Mix in 1 1/2 cups buttermilk in two installments, on a low speed.

Add in 2 tsp of vanilla extract and 2 Tbsp of vegetable oil, and mix at a low speed until fully incorporated.

Scrape down the sides of the bowl with a rubber spatula, then beat on a low speed for about 30 seconds to make sure everything is properly mixed together.

Divide the batter evenly between your prepared pans. I like to use a digital scale to make sure each pan has the same amount of batter, so that each cake layer is the same height.

Bake for 34-35 minutes, or until a toothpick comes out with a few moist crumbs. Allow the pans to cool for 10 minutes, then run a small offset spatula around perimeter of the pan to separate the cake from the pan.

Place cake layers into the freezer for 30 minutes to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers.

Use a serrated knife to level the tops of the layers right before you plan to assemble your cake, or you can wrap and freeze them in you're making them in advance.

If you make these cake layers in advance and freeze them, let them thaw for about 20 minutes before making your cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble your cake.

While the cake layers bake and cool, make the cream cheese buttercream frosting.

Beat 1 1/2 cups of unsalted butter with 1/2 cup of cream cheese on a medium speed for 30 seconds with a paddle attachment, until smooth.

Mix in 2 tsp of vanilla extract or vanilla bean paste and 1/2 tsp salt on a low speed.

Slowly add in 7 cups of powdered sugar, 1 cup at a time. Alternate with 2 Tbsp of heavy cream or milk.

Continue to mix on low speed for a few minutes, until the desired consistency is reached. 

If the frosting is too thick, add in additional cream (1 TBSP at a time). If the frosting is too thin, add in more powdered sugar (quarter of a cup at a time).

Cover with plastic wrap and set aside.

Preheat oven to 350 F (175 C).

Heavily greasing a regular sized donut pan and a mini donut pan.

Add 1 1/4 cup flour, 1 cup sugar, 1 and 1/2 tsp baking powder and 1/2 tsp salt to a large mixer bowl and gently mix. Add 1/2 cup buttermilk and gently stir until just combined.

Add in 1/2 cup water, 2 tsp vanilla and 1/4 cup vegetable oil. Mix by hand with a large spoon or whisk until the batter comes together.

Next, mix in 1 large egg until well combined.

Place batter into a piping bag, and cut a small opening (less than 1 cm). Fill the pans to make 6 normal sized donuts, and about 20 mini donuts.

Carefully pipe the batter in a circle to fill each donut mold. Fill about 1/2 full. If you overfill the pans, they will bake out of the mold and lose their perfect circular shape.

Bake regular sized donuts for 17-19 minutes, and mini donuts 12-13 minutes (or until a toothpick comes out clean).

Allow the donuts to cool before drizzle them with 2 Tbsp of honey.

Combine 1/4 cup poppy seeds, 1/4 cup sesame seeds, 1/4 cup sugar, and 1 tsp salt into a bowl, and stir until combined. Dunk the donuts into the seasoning, until the tops are coated.

Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.

Add an even layer of cream cheese buttercream between each cake layer with a large offset spatula.

Add a thin coat of frosting around the cake, fully cover the cake layers.

Smooth using a bench scraper, then chill the cake in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Add a second, thicker layer of frosting to the cake, and smooth using a bench scraper.

Chill again in the fridge (20 minutes) or freezer (5 minutes) until the frosting is firm to the touch.

Pipe or spread a thin ring of frosting around the base of the cake. Gently press the mini bagels along the bottom of the cake to create a boarded.

If desired, use the different colored fondant to make your desired bagel toppings! I made some lox, tomatoes, onions, and capers.

Add some cream cheese frosting and optional fillings into the larger bagel donuts, and place them on top of the cake. I found that adding a dab of frosting underneath each bagel helped keep it in place.