Make the buttermilk: Combine the 2 cups of lactose-free milk with 2 tablespoons of lemon juice. Set aside for at least 10 minutes.
Preheat your oven to 425 degrees F.
Line a sheet pan with parchment paper. Set aside.
In a large bowl, whisk together the flour blend, xantham gum (if using), granulated sugar, baking powder, baking soda, and salt. Set aside.
In a medium bowl, whisk together the melted and slightly cooled butter, eggs, vanilla, prepared buttermilk, and water.
Add the contents of the medium bowl (the wet ingredient) into the large bowl containing the dry ingredients, whisk to combine. Some lumps are OK!
Pour the batter onto the prepared parchment-lined sheet pan. Spread evenly. Sprinkle your add-ons on top of the batter.
Bake in a hot oven for 15 minutes, or until brown.
Remove from the oven and cut with a pizza cutter, serve with the toppings of your choice!