To make the cornbread: Heat a well-greased 10-inch cast-iron skillet in a 450 degree oven for 6 minutes.
Meanwhile in a large bowl mix together cornmeal, flour, sugar, baking powder and salt; stir in the eggs with melted butter and buttermilk; mix JUST until moistened.
Pour the batter into the hot skillet.
Bake at 450 degrees for 20 minutes or until golden.
Cool the cornbread completely, then cut into 1-inch cubes.
Arrange the cubes in a single layer on a large baking sheet.
Bake in a 350 degree oven for 10-15 minutes until lightly browned; set aside or freeze until ready to use.
For the stuffing casserole; butter a 13 x 9-inch baking dish and set oven to 350 degrees.
Melt butter in a large skillet over medium heat; add in the chopped yellow onion, jalapeno pepper, garlic, celery and cumin; saute until the onions are tender.
Add in uncooked shrimp and chopped smoked sausage, green onions and corn; cook stirring constantly until the shrimp begins to turn pink.
Remove from heat (the shrimp will still be slightly raw!) add in cilantro, milk and eggs, then season with seasoned salt and black pepper.
Fold in the cornbread cubes; toss lightly to combine.
Spoon into prepared baking dish.
Bake for about 30 minutes.
Serves 8 - 10