Place the corn directly over the fire. Cook, rotating the ears frequently, until all sides are lightly charred. Remove from the grill and let cool slightly before cutting the kernels from the ears.
Add the chicken stock and 3 tablespoons of butter to a medium sauce pan.
Bring to a boil and stir in the milk, salt and pepper.
Continue boiling while whisking in the grits. Add the corn. Cook for 10-15 minutes, stirring continuously, until the grits are creamy. You may have to add more stock or half and half if they get too thick.
Serve topped with the remaining butter and garnished with the sliced green onion.