Preheat the oven to 400 degrees Fahrenheit.
Slice butter and place in the bottom of a 9x13" casserole dish.
Place the casserole dish in the oven as it preheats.
Beat eggs slightly in medium mixing bowl. Add flour, sea salt and whole milk. Mix until all lumps are gone, and you have a smooth batter.
Once butter has melted entirely, remove casserole dish from oven.
Pour batter over the butter. I like to pour the batter in a swirling motion so that the melted butter gets mixed in to the batter.
Bake for 20-25 minutes or until edges are golden brown and batter is set.
Serve immediately.
Optional - Top with powdered sugar before serving.