Let the butter, cream cheese, eggs, and sour cream come to room temperature.

Mix the almond flour, coconut flour, psyllium fiber powder, baking powder, and salt in a small bowl and set aside.

Use a hand mixer or stand mixer to cream together the butter, cream cheese, and sweetener until smooth. The butter should lighten in color and the sweetener should be completely dissolved.

Continue using the mixer to beat in the eggs one at a time. Use a spatula to scrape down the sides of the bowl as needed.

Stir in the sour cream by hand. Add the dry ingredients and mix by hand to form a thick batter.

Measure in the vanilla extract and lemon juice and stir to combine.

Divide the batter evenly into six small bowls. Use each bowl to create the six different colors of layers. Start with the recommended drops and add color one drop at a time until the desired color is achieved. The colors should intensify after baking.

Red: 12 drops red Green: 12 drops green

Orange: 12 drops yellow & 4 drops red Blue: 12 drops blue

Yellow: 12 drops yellow Purple: 10 drops blue and 4 drops red

After each color is mixed, pour into a prepared pan and bake as directed in step 10.

Using 8" pans, bake for 10-12 minutes or until the tops are barely firm to a light touch. Let cool in the pans for about 15 minutes before inverting onto a cooling rack. Let cool to room temperature for an additional 15-20 minutes before using or wrap tightly to store in the refrigerator or freezer.

Bring the sweetener and water to a boil in a small saucepan. Continue boiling until the syrup reaches a temperature of 245-250 degrees F (about 3-4 minutes after the mixture begins to boil).

While the syrup comes to a boil, place the egg whites in the bowl of the stand mixer. Use the whip attachment to whip the egg whites on low speed until foamy. Sprinkle in the cream of tartar and increase the mixer speed to medium high until stiff peaks form.

With the mixer running on low, slowly pour the syrup into the beaten egg whites in a slow and steady stream. Use caution to avoid burns. Increase speed to high and continue beating until the mixture begins to cool, about 7-10 minutes. Use the thermometer to add the butter when the mixture has cooled to about 80-85 degrees F.

Continue whipping the mixture and begin adding the butter one tablespoon at a time. Wait 20 seconds or so between adding each tablespoon of butter. The butter will gradually cool the mixture so the temperature of the egg whites and the butter are both very important. If the egg white mixture is too warm, the buttercream becomes a soupy mess. If the butter is too cool, the mixture will clump.

After the butter is added, continue whipping for another minute or two. Stop the mixer, scrape the sides of the mixing bowl, add the vanilla extract and salt, and mix for one more minute.