Stir together your cream cheese, vegan cream, vinegar, and vanilla and set aside.*
Whisk together your flour mix, xanthan gum, baking pwder, baking soda, and salt in a mixing bowl.
Put the cold margarine, shortening, and sugar into your food processor with the blade. Turn it on and let it run until they are fully combined, about 15-20 seconds.
Add the cream cheese mixture to your food processor and run it until they are combined.
Put the dry ingredients in the food processor and run for another 15-20 seconds, until it comes together as a dough.
Turn the dough out of the food processor onto your counter and knead it together a few times to make sure everything is mixed in. Press 2/3 of the dough into your prepared pan, wrap the rest in plastic wrap, and put it all in the fridge for 1-2 hours.
Once the dough has chilled, preheat your oven to 350*F.
Stir together your filling ingredients and and spread it across your prepared base. Put small pieces of the remaining dough across the top of the blueberry filling. Bake for 45-50 minutes. Put the pan on a wire rack to cool, then refrigerate overnight before serving.
Once the bars have cooled, make the glaze by whisking together all of the ingredients in a small mixing bowl. If needed, add more water to the sugar to reach your desired thickness. Put it in a small piping bag or a zip-top bag, snip the tip off, and drizzle it over the bars.
Notes
*You can replace the dairy free cream cheese and cream with Greek style yogurt.