Preheat the oven to 425F. Lightly grease a 12? cast iron skillet or large round baking pan with butter. Set aside.

In a large bowl, whisk together the cake flour, all-purpose flour, sugar, baking powder, baking soda, and salt.

Add in the cubed butter, and use a pastry cutter or two knives to cut the butter into the flour mixture until it is crumbly and resembles pea-sized chunks.

Make a well in the center of the mixture, and pour in the buttermilk and sourdough discard. Mix with a wooden spoon until barely combined.

Use your hands to knead and fold the dough over itself a couple of times until combined.

Add the blueberries, and gently fold a few more times until the blueberries are evenly dispersed.

Use a very large cookie scoop or a ? cup measuring cup to scoop the dough for each biscuit, and place in the prepared skillet or pan.

Mix together the brown sugar and cinnamon in a small bowl for the cinnamon sugar topping.

Brush the tops of the biscuits with buttermilk or heavy cream. Then, sprinkle the tops with the cinnamon sugar mixture.

Bake for 20-25 minutes, or until fluffy and golden brown.

While baking, prepare the whipped salted vanilla bean butter by whipping the butter and vanilla bean paste together until combined and fluffy.

Remove the biscuits from the oven and serve warm with the whipped salted vanilla bean butter, honey, and flaky sea salt if desired.