Step 1Cook the grits according to the package directions and set aside in a warm spot.
Step 2Thinly slice the shiitakes (if the caps are very large, cut them in half and then into slices). Melt the butter in a large deep skillet over medium-high heat. Add the shallots and garlic. Stir in the herbes de Provence, sprinkle in the salt and cook, stirring, 1 to 2 minutes. Stir in the shiitakes and cook, stirring constantly, until the mushrooms are tender and lightly browned, about 5 minutes.
Step 3Immediately add the soy sauce, stirring to loosen the browned bits on the bottom of the pan. Stir in the Worcestershire sauce, mustard and Tabasco to taste, mixing well. Add the stock and cook, stirring, just until the mushrooms are coated and a thin sauce forms.
Step 4Ladle the grits onto serving plates and spoon the shiitakes over them. Sprinkle with the chives.