To make the Low Carb Cake: Beat eggs, add cream, water, vanilla and swerve. Then add the remaining ingredients. Blend well. Divide batter between 2 prepared pans. Cover each pan with aluminum foil.
Place 1 cup of water in your pressure cooker and your rack. Carefully stack cake pans in your pressure cooker. If you pans do not have a lip making stacking possible, use broken bamboo skewers laid across the bottom pan to support the top pan.
Cook your cakes under high/standard pressure for 25 minutes. Allow to naturally depressurize.
Remove cakes from your pressure cooker and invert on a cooling rack (removing pans) and allow to cool completely before frosting.
For the Raspberry Buttercream: Using a stand or hand mixer, beat softened butter on high speed until light and fluffy (about 3 minutes) Add powdered swerve, 1/2 a cup at time, until completely incorporated. Add in raspberry powder and heavy cream.
Use roughly 1/3 of the frosting in-between the cake layers, then the rest to frost/decorate.
Using a low-carb powdered sugar substitute will produce a slightly grainer buttercream that when using regular powdered sugar.