• Set the oven to 350°F / 180°C and prepare two 9-inch round cake pans with parchment circles on the bottoms and well-greased sides. The parchment should sit flat so the delicate layers release more easily.
• Whip the softened cake butter with the 1 cup powdered sweetener in a large mixing bowl. Stop when the mixture looks pale and fluffy, with no obvious butter lumps.
• Beat in each egg separately before adding the next. The mixture should become evenly blended after each addition rather than showing streaks of egg.
• Turn the mixer to low and incorporate the apple cider vinegar, vanilla extract, and heavy whipping cream. A slightly separated appearance at this stage can settle once the flours enter the mixture.
• Work the almond flour into the wet mixture in several additions using low speed. Each addition should disappear into the batter before the next goes in.
• Mix in the coconut flour, cocoa powder, and baking powder just until evenly incorporated. Look for a cohesive batter with a silky surface and a slightly thick consistency.
• Tint the batter gradually with the red food coloring, stopping at your preferred shade. Color strength varies by product, so judge the batter rather than adding the full amount automatically.
• Portion the batter equally into the two pans and level each surface. Even batter depth helps both layers bake at a similar pace.
• Bake the layers for 20 to 25 minutes, checking the centers before removing them. The tops should look set, and a toothpick should carry a few damp crumbs without wet batter.
• Leave the baked layers in their pans until completely cool. The pans support the tender cakes while their structure firms.

Make the Keto Cream Cheese Frosting

• Whip the cream cheese, frosting butter, powdered sweetener, and vanilla extract in a large bowl at medium speed for about 3 minutes. The finished frosting should look fluffy and uniform, without visible pieces of butter or cream cheese.

Assemble and Frost the Cake

• Center the first cooled layer on a serving plate or cake stand and cover its top with about half the frosting. An even filling gives the upper layer a level surface to rest on.
• Stack the second layer and use an offset or icing spatula to spread the remaining frosting across the top and around the sides. Light pressure helps keep loose crumbs from dragging through the frosting.
• Chill the assembled cake in the refrigerator for at least 60 minutes before cutting. The frosting should feel firmer and hold the layers steady.
• Cut the chilled cake into slices and serve. The filling should stay between the layers rather than squeeze out beneath the knife.