Serve a big batch of these flaky and tender buttermilk biscuits baked in hot, buttered cast iron skillets for breakfast, lunch, or dinner.
Preheat oven to 425 degrees F (220 degrees C). Place 1 tablespoon butter in two 10-inch cast iron skillets.
Place skillets in the preheated oven to heat up and melt butter, 5 to 10 minutes.
Mix buttermilk and eggs together in a small bowl.
Combine flour, baking powder, cream of tartar, and salt in a large bowl. Rub in remaining 6 tablespoons butter with your fingers until mixture is crumbly. Gently stir in buttermilk mixture until dough just starts to come together.
Turn dough out onto a lightly floured work surface. Pat into a rectangle about 1/2 inch thick. Cut dough into 24 biscuits.
Remove skillets from the oven. Arrange 12 biscuits side-by-side in each, their edges touching.
Return skillets to the oven and bake until biscuits are puffed and lightly browned, 15 to 20 minutes.