Melt 1 cup butter in a medium saucepan over medium-high heat. Swirling occasionally, continue to cook until fragrant and browned. The butter will foam up a bit and little bits of browned butter will sit at the bottom of the pan when done. Remove from heat and transfer to a heat-safe container. Chill until the consistency of softened butter.
Pre-heat oven to 350 degrees. Grease and flour three 8-inch cake pans and set aside.
Sift together the flour, baking powder, salt, cinnamon, ginger, nutmeg and cloves. Set aside.
Place browned butter in the bowl of an electric mixer. Using the paddle attachment, mix until smooth. Add in the granulated sugar and brown sugar. Increase speed to medium-high. Continue to mix for about 3-5 minutes. Stop the mixer and scrape down the sides and bottom of the bowl.
With the mixer on medium-low, add in the eggs, one at a time. Add in vanilla. Once incorporated, stop the mixer and scrape down the bowl.
With the mixer on low, add in the flour mixture and milk in three alternating additions – starting and ending with the flour mixture. Mix on medium-low for now more than 30 seconds or until combined.
Evenly distribute the batter between the three pans. Bake for about 23-25 minutes or until a toothpick inserted into the center of the cakes comes out clean or with few crumbs. Cool on a wire rack for 10-15 minutes before removing the cakes from their pans.
Make the Eggnog Buttercream Filling:
Place the cream cheese and butter in the bowl of an electric mixer. Mix until smooth. With the mixer on low, gradually add in the remaining ingredients until incorporated. Turn up the mixer to medium-high and mix until light and fluffy.
Make the Vanilla Swiss Meringue Buttercream:
Place the egg whites and sugar in the bowl of an electric mixer. Whisk to combine. Fill a medium saucepan with a few inches of water and place over medium heat. Place the mixing bowl on top of the saucepan to create a double-boiler. Whisking intermittently, heat the egg white mixture until 160 degrees on a candy thermometer.
Once hot, transfer the mixing bowl back to the electric mixer. Using the whisk attachment, whip the egg white mixture on high for 8 to 10 minutes until the outside of the mixing bowl returns to room temperature and the egg whites are fluffy, glossy and hold a stiff peak. Stop the mixer and swap out the whisk for the paddle attachment.
With the mixer on low, add in the remaining ingredients. Once incorporated, whip on medium until silky and smooth, about 3 to 5 minutes. The buttercream may look like it’s curdled or soupy. Keep mixing until it is completely smooth.
Assemble the Cake:
Once the cakes are cooled, trim the tops as needed to level using a large serrated knife. Place the bottom layer of cake on a cake board or serving dish. Spread on about 1 cup of eggnog buttercream with an offset spatula. Top with the next layer of cake and repeat. Crumb coat and frost the cake with the vanilla buttercream. Create swirls using the rounded tip of an offset spatula while spinning the cake. Garnish with toffee bits, if desired.
Best served at room temperature so that the buttercream is silky smooth.
If serving the day that it is made, cake may be kept at room temperature. Refrigerate leftovers, loosely covered in plastic.