Preheat oven to 425°. Spray wells of an 8-well cast-iron wedge pan with cooking spray.
For biscuits: In a large bowl, whisk together flour, chives, baking powder, salt, onion powder, baking soda, garlic powder, and pepper; stir in cheese.
In a small bowl, combine buttermilk and 3 tablespoons melted butter. Make a well in center of flour mixture; stir in buttermilk mixture until dry ingredients are moistened. Spoon about ⅓ cup dough each into 4 wells of prepared pan.
Bake for 8 minutes.
For frittata: In a medium bowl, whisk together eggs, milk, and mustard until frothy; stir in spinach, ¼ cup artichoke hearts, chives, salt, and pepper. Carefully divide egg mixture among remaining 4 wells. Top egg mixture with remaining ¼ cup artichokes.
Bake until biscuits are lightly browned, frittatas are puffed, and a wooden pick inserted in centers comes out clean, about 12 minutes more. Let cool in pan for 10 minutes. Brush biscuits with remaining 1 tablespoon melted butter. Serve immediately.
Recipe by Southern Cast Iron at https://southerncastiron.com/artichoke-frittata-cheese-biscuit-wedges/