Prepare a pan with simmering water fitted with another pan over the top (Bain Marie).
Do not allow the surface of the water to touch the bottom of the top pan.
To the top pan (a metal mixing bowl works great for this purpose) add 2 egg whites (be sure there are no yolks), a dash of coconut cream, 1 tsp water and the remaining of xylitol.
Whisk this mixture continuously for 5-10 minutes over the water bath until all the xylitol has dissolved.
Pour this mixture into a separate bowl and whip with a blender until stiff fluffy peaks form.
Add 1 tsp vanilla, blend to incorporate. The frosting may be used, as is, immediately (it does not store well) as a marshmallow frosting – dust the cupcakes with cinnamon as a garnish.
For butter cream frosting: continue to beat on medium speed, begin adding about ½ cup butter 1 tbsp at a time (allow to beat for 1 minute in between each addition of butter).
The frosting may break down and get soupy looking, continue to add butter and beat until it comes together (more butter may be necessary, 1 tbsp at a time).
Add 1-2 tsp cinnamon (to taste, optional) and blend to combine.
Buttercream should be used immediately by piping onto the cooled cupcake with a pastry bag and fancy tip or by simply cutting the corner of a plastic bag.
Buttercream frosted cupcakes may be refrigerated in an airtight container for up to 5 days.
Serve at room temperature dusted with cinnamon.