Heat your oven to 400 degrees and line a baking sheet with parchment paper.
In a large bowl, whisk the flour, sugar, baking powder,xantham gum (if using)and salt.
Grate the butter using a cheese grater and add it in. Use your hands to blend the butter in to the flour mixture until it looks like coarse sand. A pastry cutter works too.
In a separate medium bowl, whisk the egg, milk, lemon juice, lemon zest and vanilla.
Add the wet ingredients into the dry ingredients and mix. Stir in the blueberries and stir until well mixed.
Pour the dough onto the pan and shape into a circle about 8 inches in diameter (it will be sticky.) Use a sharp knife or bench scraper to cut the scones into 8.
Brush the tops with cream and sprinkle with the cane sugar
Refrigerate for at least 15 minutes.
Once chilled, bake until the edges are deep golden brown and the tops are light browned, about 30-40 minutes, depending on your oven.
Let cool completely on the pan.
Once cooled, whisk together the glaze ingredients and drizzle on the scones.