Draw three 9 inch circles with a marker on a piece of parchment paper. Flip the paper over so you aren’t placing the cake onto ink. Place the parchment onto a large baking sheet. Set aside.
Place the egg whites, sweetener, salt and cream of tartar into a stand mixer (or large bowl) and mix on high speed until stiff peaks form, about 5-7 minutes. Add the Further Foods collagen, poppy seeds and lemon zest and stir to combine. Room temperature eggs will whip better and faster.
Evenly distribute the meringue mixture onto the three circles on parchment paper. Form the mixture into three cake layers that are 1 inch high circles that are evenly shaped. Flatten the top so the layers sit on top of each other easily when you assemble the cake.
Place the baking sheet into the oven and bake for 3 hours. After 3 hours, turn the oven off and allow the meringue to dry in the oven.
Meanwhile make the filling.
For Lemon Curd: Combine natural sweetener, lemon juice, 4 eggs and lemon peel in heavy medium saucepan and whisk to blend; add coconut oil. Whisk constantly over medium heat until mixture thickens and coats back of spoon thickly (do not boil), about 12 minutes. Pour mixture through strainer into medium bowl. Place bowl in larger bowl filled with ice water and whisk occasionally until lemon curd is cooled completely, about 15 minutes. Can be made 1 day ahead.
For Protein Sparing Filling: Place all the ingredients into a blender and puree until very smooth. Taste and adjust sweetness to your liking.
Place the bowl in the fridge until cakes are cooled.
To assemble, place the one meringue layer on a cake platter. Use a piping bag if you want to be fancy (or use a knife) to spread 1/3 of the lemon curd filling over the first layer. Top with a layer of raspberries. Repeat with remaining cake, filling and raspberries.
Photograph your cake now because once it is cut, it isn't as beautiful, but it tastes great! Use a very sharp knife to cut into slices and serve.