Trim the tough skin and membrane from the monkfish and cut into 4 equal portions. If you can get your fishmonger to do this for you, even better.
Combine, the garlic, herbs, and a little salt and pepper in a mixing bowl. Toss the fish in the herb mixture to coat evenly.
Heat a large saute pan over medium high heat. Put in a good amount of olive oil. Place the fish in the pan when hot. Sear one side until lightly browned, then turn over and sear the other for about a minute.
Transfer the fish to a flat pan sprayed with pan spray, place in 350 degree oven to finish, about 10 minutes. You can check the temperature with a meat thermometer. It should be 145 to 155 degrees.
Start the sauce before putting the fish in the oven and make it while the fish is roasting. You can use the same pan as the fish if there aren't too many stray herbs that will burn in the pan. Or you can wipe it out and start fresh.
Heat a saute pan and add in the bacon pieces, render until it becomes brown and the fat is liquid. Drain off some of the fat if it looks like too much. Add in the leeks and stir occasionally. Cook until they become translucent. Then add the wine and cook it down by 1/2 volume. Add in the stock and reduce that by 1/2. Before you serve, whisk in the butter a little at a time so it blends in, but doesn't separate. It will create a creamy sauce. You don't want it to melt and separate.
Continue whisking and add in the lemon juice, salt, and pepper. Make the sauce as close to service as possible. If you try to reheat it could "break" and separate into liquid and melted butter. This is why the butter is added last (with the seasoning and lemon juice).
For the Puree: Boil potatoes in lightly salted water.
When they are fully boiled, soft to the touch, but not falling apart, strain them.
Toss the cauliflower in a little oil, salt, and pepper and roast in the oven for 10 to 15 minutes. They should be soft to the touch.
Put the cauliflower into a food processor while still hot. Puree until smooth, scraping down the sides occasionally. Add in the potatoes and follow the same procedure. Be careful how long you puree for. The potatoes can become gummy.
With the machine running, add in the butter, continue pureeing. Add in salt and pepper to finish and transfer to a bowl (or pan if it needs to be reheated) and test to make sure the seasoning is good and it's not too thin.
For the brussel sprouts, heat oil in a pan over medium high heat. Add in the brussels and allow them to get some color on one side, Then toss or stir to get color on both sides. Stir often to keep from over cooking. They should still be firm. Add sugar and stir. Allow the sugar to melt. Then add the lemon juice and cook down. If the brussels are still undercooked you may add a little water. The liquid should be mostly gone except for a light glaze. Add salt and pepper. Stir that in.
To Plate: Spoon the Cauliflower puree unto the plate and drag it a bit to make a trough to put the fish on. Alternatively, you could mound the puree to give the dish height. Place the fish atop the puree. Arrange the Brussels around the puree. Spoon the sauce over the fish and then garnish with lemons and herbs or microgreens. Enjoy with a lighter ale, like Harp or Smithwicks or a nice white wine.