Step 1 Heat the oven to 450 degrees. In a large bowl, whisk together the cornmeal, flour, sugar, baking powder and salt. In a separate bowl, whisk together the eggs and milk. Fold the wet ingredients into the dry ingredients, then fold in the clarified butter. Transfer the mixture to a blender and blend to fully incorporate the ingredients.
Step 2 Heat a small (5- to 6-inch) cast iron skillet over medium-high heat until hot. Add a small pat of butter to the pan, swirling the pan until the butter is melted and bubbly. Spoon in about 3/4 cup batter, spreading the batter so it reaches the edges of the pan in an even layer.
Step 3Cook the batter in the pan until the bottom forms a crust and the batter begins to bubble around the edges, about 2 minutes. Transfer the pan to the oven and bake until the cake is almost set but jiggles slightly in the center, 2 to 3 minutes.
Step 4Return the pan to the stove-top and flip the cake over in the pan. Continue cooking over medium-high heat until the cake is set and a crust has formed on the bottom of the cake, 1 to 2 minutes. Remove from heat.
Step 5Spread 2 to 4 tablespoons maple butter over the cake, sprinkle over a little coarse sea salt and garnish with green onion. Serve immediately.