Preheat the oven to 450℉.
In a bowl, mix together the flour, salt, sugar, lemon zest and baking powder. Then, add in the buttermilk and stir until everything is combined. Lastly, fold in the blueberries.
Place the baking dish in the oven with the 6 TB of butter and allow to melt. This also preheats the baking dish to help with the crispy edges.
Once the butter is melted, remove the dish then add in the biscuits mix. Carefully spread it out in the baking dish then using a knife, score the biscuits into 9 squares 3x3.
Place the dish back into the oven and bake for 20-25 minutes. The biscuits are done when the tops are golden but you can push it a little longer if you like a lot of browning on the top.
When done baking, remove the biscuits from the oven.
Mix together the ingredients for the icing then pour on top of the hot biscuits and spread it out evenly over the biscuits.
Once the biscuits are cool, slice and serve.