Preheat oven to 450 degrees F and move oven rack to center position.
When oven is completely preheated, place cast iron in oven for five minutes. While pan heats make the batter. Melt 2 Tablespoons butter. Add melted butter, milk, flour, eggs, honey, lemon zest, vanilla and salt to blender. Blend until smooth.
Remove pan from oven, add 2 tablespoons butter. Use a fork to move the butter around the pan coating the bottom and sides of pan. Add blueberries to pan, immediately pour batter into the pan in a circular motion to sort of spiral the batter from the center to the edges. This helps to keep all the blueberries from going to the edges. Immediately place pan in oven. Bake for 15 minutes. Remove from oven. Top with butter, real maple syrup and/or berries if desired. Enjoy!