PRE-HEAT OVEN TO 450º
TRIM LEAVES FROM THE CAULIFLOWER. TRIM AN INCH OFF THE STEM. CUT OFF THE FLOWERETS. SLICE THE LARGE ONES AND THE STEM INTO 1/2 THICK PIECES.
PLACE IN A STEAMER, COVER AND STEAM FOR 6 TO 8 MINUTES OR UNTIL THE THE PIECES ARE A LITTLE UNDERDONE.
USING A SMALL PIECE OF WAXED PAPER, BUTTER THE INSIDE OF AN AU GRATIN DISH. CUT THE GARLIC CLOVE IN HALF. SCATTER SOME SALT INSIDE THE DISH AND RUB THE GARLIC INSIDE THE PAN.
USING THE LARGEST HOLES ON A BOX GRATER, GRATE THE GRUYÈRE. FINELY GRATE THE PARMESAN.
COMBINE THE CREAM AND CRÉME FRAÎCHE TOGETHER IN A BOWL. STIR IN THE CHEESES.
ARRANGE HALF THE STEAMED CAULIFLOWER IN THE AU GRATIN DISH. USING A SPOON OR YOUR FINGERS, SPREAD HALF THE CHEESE MIXTURE OVER THE CAULIFLOWER. LAYER THE REST OF THE CAULIFLOWER ON TOP, THEN THE REMAINING CHEESE MIXTURE. SALT AND PEPPER.
PLACE THE AU GRATIN DISH IN THE TOP THIRD OF THE OVEN. COOK FOR ABOUT 20 MINUTES OR UNTIL THE CAULIFLOWER IS BROWNED ON TOP.
SCATTER WITH FRESHLY CHOPPED CHIVES AND SERVE.
SERVES 6