Preheat the oven to 400°F.
Lightly grease a large oven-proof skillet.
In a large mixing bowl, combine the all-purpose flour, baking powder, salt, and sugar.
Add the softened butter pieces to the flour mixture.
Using your hands, gently work the butter into the dry ingredients until the mixture becomes crumbly.
Add the buttermilk to the flour mixture.
If using the buttermilk substitute, combine the milk and apple cider vinegar first and allow it to sit for several minutes before adding it to the flour mixture.
Mix gently until the dough is just combined.
Fold in the frozen blueberries carefully, taking care not to crush them.
Transfer the dough to a lightly floured work surface.
Gently flatten the dough with your hands.
Using a 3-inch biscuit cutter, cut out the biscuits.
Place the biscuits into the prepared skillet.
Bake for approximately 30 minutes, or until the biscuits are golden and cooked through.
While the biscuits are baking, prepare the glaze.
In a small bowl, combine the powdered sugar, heavy cream, vanilla extract, lemon zest, lemon juice, and ground cinnamon.
Stir until the glaze is smooth and pourable.
Remove the biscuits from the oven.
Drizzle the glaze over the warm biscuits.
Serve warm.