Bring 6 cups water to a full rolling boil in a heavy 4-quart saucepan. Add 1 Tbsp salt; slowly add grits, pouring them into pan in a thin, steady stream while whisking constantly. Reduce heat to low; simmer, stirring occasionally, 5-7 minutes, until grits have thickened. Stir in half-and-half and butter (it will seem very thin but grits will thicken again as they cook). Bring to a boil over medium heat. Reduce heat, cover and simmer 45 minutes or until smooth and creamy, stirring occasionally. Remove from heat. Stir in Roquefort, 1 tsp salt and 1 tsp pepper. Serve hot.