Beef Wellington with Dijon Cognac cream sauce

Clean the mushrooms by rubbing with a clean kitchen towel; never rinse them, as they soak up water and turn spongy and bland.

Rough chop and process with shallots and garlic in batches until very finely chopped.

Melt butter with a little olive oil in a skillet, not screaming hot. Add the mushroom mixture, fresh thyme, salt and pepper and cook about 10 minutes, until there are no visible moisture bubbles and it is a deep brown paste.

Heat the cast iron skillet until smoking hot with a small drizzle of light olive oil or avocado oil.

Season the board with lots of coarse kosher salt and freshly ground black pepper. Tie the fillet in a few places to keep its shape and roll it in the seasoning.

Sear the fillet without flipping until each side, ends included, is deeply golden brown and crusty. Remove to a plate and let cool.

Overlap a couple of layers of plastic wrap and lay overlapping prosciutto on top, as long as the roast. Spread the mushroom filling over it in one thin, even layer.

Cut the string off the roast and spread a thin layer of whole grain Dijon mustard over it, flipping to coat the underside.

Use the plastic wrap to lift the prosciutto onto the beef and roll it up; wrap in the plastic and refrigerate 20 minutes.

Open both sheets of thawed, cold puff pastry on a little flour, overlap them slightly and seal together with egg wash, one egg beaten with a touch of water. Roll out.

Roll the beef up in the pastry; trim excess if wanted, seal with a little egg wash, stretch the top over and tuck.

Shake off excess flour, cover lightly with plastic wrap and refrigerate about 20 minutes so the dough is cold going into the oven. Preheat the oven to 400.

Score a light pattern on top, which also vents it; skip a doubled lattice, which leaves the pastry raw. Brush the top.

Rest on a wire rack about half an hour; carryover cooking takes it 25 to 30 degrees higher, to about 145.

Insert a probe thermometer in the center. Bake at 400 about 40 to 45 minutes, until it reads 120 (around 105 for rare); tent with foil or turn the oven down if the top gets too dark.

For the sauce, soften very finely chopped shallots in a tiny bit of butter in a small saucepan without much color. Add the cognac and reduce by half.

Add the beef stock, heavy cream, a pinch of salt and lots of coarsely ground black pepper; cook until it coats the back of a spoon.

Slice the Wellington carefully on a cutting board and serve with the sauce.

Stir whole grain Dijon into the thickened sauce and whisk.