Preheat oven to 425°. Make sure that your cast iron skillet is in the oven while it's preheating so it gets hot.
In a large bowl combine two and a half cups of sourdough discard, 1/4 cup honey, 1/2 cup kefir, 6 eggs, and ½ tsp of salt.
Add baking soda to the mixture, stirring thoroughly to break up the baking soda. The mixture will bubble and rise.
Stir in 1 cup of frozen blueberries. Because they are frozen, your batter will turn a purple shade.
When the oven has come to temperature, remove the hot skillet from the oven and place on the counter. Working quickly so it doesn’t cool down, drop 1 tbsp of oil or butter into the skillet (I use bacon grease).
Using a spoon or spatula, spread the oil around the skillet including up the sides.
Pour the batter into the hot skillet and return to the oven.
Bake for 25 minutes. The pancake will get a dark golden brown color on the top, it’s because of the baking soda.
Serve immediately