Preheat oven to 325 degrees F. Generously butter two round 8-inch nonstick cake pans. If your pans are not brand new and super nonstick, line their bottoms with a parchment circle and grease the parchment too.
In a large bowl, whisk together the eggs, milk, melted butter, vanilla, and stevia.
Add the almond flour, mixing it in with a rubber spatula and then whisking until batter is smooth. Whisk in the kosher salt and baking powder.
Divide the batter evenly between the two pans. To ensure the cake layers are the same size, it’s best to use your kitchen scales and weigh the batter as you pour it into the pans. I weighed each cake at 360 grams.
Bake the cakes in the middle of the oven until slightly puffed and set and a toothpick inserted in center comes out clean, 15-18 minutes. The tops of the cakes won't brown even when they are fully baked.
Remove the cakes from the oven and place them on a wire rack. Let cool for 10 minutes in the pans, then invert directly onto the wire rack, as shown in the video. Let cool completely, at least 30 more minutes.
While cakes are cooling, prepare the frosting:
Place the softened unsalted butter, heavy cream, cocoa powder, vanilla, and stevia in a medium bowl. Using a handheld electric mixer, beat on low to incorporate, then beat on medium about 1 minute, until frosting is light and fluffy.
Assemble and frost the cake:
Place one of the cake layers on a cake plate, flat side up. To keep the plate clean, you can line the plate with strips of wax paper to protect the plate (let them overhang), then pull them from underneath the cake once you’re done frosting it.
Place 1/3 cup of frosting in the middle of the cake and use an offset spatula to spread the frosting all over the top of the cake.
Gently place the second cake layer on top of the first one, flat side up. There’s no need to press on it. Place another 1/3 cup of frosting on top of this second cake, and use the spatula to spread it all over the top of the cake.
Use the remaining frosting to frost the sides of the cake, as shown in the video.
Once frosted, you can cut the cake and serve it. Or refrigerate it, covered, until ready to serve. Take it out of the fridge 2 hours before you plan on serving it.