Preheat oven to 425 degrees F. If using a 10" cast iron skillet, place on stove burner and set to a low temp to begin heating the pan up. (If you're using a 9x13 pan, spray with non-stick spray and set aside.)

Beat egg in a medium sized mixing bowl. Stir in buttermilk and vanilla. Add flour to buttermilk mixture about 1/3 of the total amount at a time, stirring until combined between each addition.

Combine baking powder, baking soda, salt & sugar. Pour onto dough. Slice 4 TBSP butter into several small cubes. Mix with a fork until everything is incorporated.

Add in blueberries and stir to combine. Place remaining 2 TBSP butter in whatever pan you're cooking the biscuits in. (I love using my 10" cast iron skillet. If you'd like, you can also use a 10" springform cake pan or even a 9x13 pan.) You want to place biscuits in a hot pan where you've melted the 2 TBSP butter, so if you're using cast iron, you can pre-heat the pan on the stovetop. All other pans need to be placed in the oven with the butter, then remove once butter is melted.

Scoop out about 3 TBSP worth of dough. And arrange in the melted butter around the pan.

Serve warm, topped with a simple glaze if desired.

Simple glaze: Whisk together 1/2 cup powdered sugar + 2 TBSP melted butter + 1 TBSP milk. Drizzle on top of warm biscuits.