Combine the crust ingredients in a food processor and pulse until the dough forms a ball. This may take 2-3 minutes. Chill the dough while you make the fillings.
To make the strawberry and/or blueberry filling heat the berries and sweetener over medium heat until the sweetener dissolves. Transfer to a small blender or food processor and process until smooth. Add the xanthan gum.
To make the brown sugar cinnamon filling simply stir together the ingredients.
Preheat the over to 350.
Roll out the dough between two pieces of greased parchment paper. Cut 2x3 inch rectangle with a pizza cutter. Reroll the extra dough and make more rectangles until it is all used up.
Place one piece of the parment you were using on a cookie sheet. Gently transfer half of the rectangles to the prepared baking sheet.
Top each of the bottom rectangles with a tablespoon of filling. Cover with a top rectangle. Press the edges together with your fingers. Use a fork to poke a few holes in the top of the pastry and to crimp the edges.
Bake for 15-20 minutes or until golden brown. Top with icing and sprinkles if desired.
Mix together the powdered sweetener and butter. Thin with almond milk a little at a time until you reach a spreadable consistency. Spread on the cooled pop tarts.
