Pre-heat oven to 350 degrees. Grease a long, rectangular tart pan with coconut oil and set aside.
Mix almond flour, arrowroot flour and salt. Add egg and butter, then mash crust together using a fork until small crumbs form and flour is just combined.
Press crust into prepared tart pan using fingers and pushing crust up the sides of the pan. Ensure the crust is about 1/4″ thick throughout (including at the top of the pan sides).
Bake crust at 350 degrees for 15-20 minutes or until it begins to turn golden brown (don't over cook or it will crack).
Combine cranberries, monkfruit sweetener, marmalade, orange juice and cinnamon stick in a saucepan over medium-low heat. Stir frequently until sweetener is dissolved and continue simmering for 12-15 minutes until the cranberries have softened but are not bursting.
Remove cranberry mixture from heat and allow to cool slightly. While cranberries cool, sprinkle gelatin into cold water and allow to rest for 2-3 minutes. Stir gelatin into cranberry mixture and allow to cool completely. Once cranberry mixture has cooled, pour into baked and cooled tart crust (put the tart crust on a pan or sheet of foil in case it leaks).
Refrigerate tart for at least one hour before serving.
If using the protein frosting, mix yogurt and casein protein together until smooth. Spoon into a piping bag and pipe about 2 tbsp of the mixture on top of each tart slice (whipped cream style!).