Spray a large casserole dish with non-fat cooking spray. Add cauliflower florets to dish and lightly coat them with non-fat cooking spray. Then season with half the salt and pepper. Put into oven and roast for 25 minutes or until cauliflower is golden brown.
Meanwhile, whisk flour with 2 tablespoons buttermilk until smooth.
Heat the wine and remaining buttermilk in a saucepan over medium heat until steaming. Add the flour mixture; cook, whisking, until the sauce bubbles and thickens, 2 to 3 minutes.
Remove from heat; stir in Gruyere, chives, shallots, garlic, salt and pepper. Spoon over the cauliflower and serve.