Even though it's definitely made of cauliflower (yeah, you can catch a whiff), when you're eating it, you can almost forget and think you're having an ooey gooey casserole.
2 heads cauliflower (about 4 lbs total)
1 stick butter
1/2 c panko (or other bread crumbs, the lighter the better)
1 c grated Parmesan
salt & pepper
1/2 t ground mustard
good shake or two cayenne
2 t cornstarch dissolved in a bit of water (originally called for 1 t... but I wanted a little more thickening)
1 T fresh chives (I skipped)
Put rack in middle of oven. Preheat to 400 F.
Prep cauliflower: Remove outer leaves and cut around core with paring knife to remove. Cut stem into thin slices. Cut head into 1/2" slabs. Cut stems from slabs to make florets that are about 1.5" tall. Slice stems thinly and add to core. [You should end up with about 3 cups of stems/cores and 12 c florets.]
Combine stems, cores, and about 2 c florets with 3 c water (I'm going to try 2.5 c next time) and 6 T butter (3/4 the stick) in the bottom of a Dutch oven. Cover, bring to boil and cook about 10 minutes. **(Start Breadcrumbs)** Add steamer basket and florets, put lid back on and steam for 10-15 minutes until you can easily put a paring knife into the stem ends of the florets. Remove from heat.
Breadcrumbs: Melt 2 T butter in 10" nonstick skillet over medium heat. Add panko and cook, stirring frequently, until golden brown. Remove from heat. When cool, add 1/2 c Parmesan and stir. I stir in a good bit of garlic salt just because.
Place florets in a large bowl. Put butter & stems in a food processor (can hold some liquid in the pan if you're in danger of overflowing. Add 2 t salt, 1/2 t black pepper, 1/2 t mustard, cayenne, and 1/2 c Parmesan. Process until smooth and velvety, about 1 minute. Mix cornstarch with a little water and add to processor while it's running. Taste and adjust seasoning. Add puree to florets (with remaining cooking liquid if you held some back) and toss gently. Transfer to a 9"x13" baking dish. Smooth top.
Bake, uncovered, 10 minutes. Sprinkle bread crumbs on top and return to oven for another 5-10 minutes, until gratin is bubbly around edges and crumbs are deep golden and lovely. Let stand 20 minutes before serving. Sprinkle chives on top.