Fresh snipped rosemaryto taste, about 1 teaspoon is what I used
For the Filling
½cupfinely diced fennel
½cupfinely diced onion
2clovesabout 1 teaspoon minced garlic
1tablespooneach extra virgin olive oil and unsalted butterdivided
2tablespoonsminced fresh parsley
1teaspoonfresh minced thyme
½cuppankoor fresh breadcrumbs if desired
Chicken stock as needed to moisten the stuffing
For the Mustard Sauce
1cupchicken stock
2teaspoonscorn starch
2tablespoonsDijon mustard
¼cuplow-fat milkor half and half (if you're not counting)
Salt and freshly ground pepperto taste (well duh)
Instructions
Heat the oven to 350°FPrepare the TenderloinTrim all the silver skin from the tenderloin and butterfly it. Place between two pieces of plastic wrap and using a flat meat pounder, or the bottom of a small skillet, gently pound the meat, working from the middle to the outside, until it is uniformly even about ⅓ inch thick. Season with salt and freshly ground pepper; thinly spread the mustard over the surface then snip the rosemary finely over the top.
Prepare the Stuffing: Heat half the oil and butter in a skillet, when the butter has melted add the fennel, and onion, sauté stirring until the onion begins to turn translucent, add the garlic and cook for 1 minute more. Add the fresh herbs, cook for 1 minute, then add the bread crumbs, stir well; add enough chicken stock to just moisten the bread crumbs (omit this step if using fresh). Taste and adjust for salt and pepper. Spread evenly over the tenderloin. (if not cooking immediately, make sure the stuffing is completely cool before spreading so no bacteria begins to form). Roll tightly jelly-roll fashion, and tie at 2-inch intervals with cooking string. Season with salt and freshly ground pepper.
Heat the remaining oil and butter together in an oven-proof skillet, when hot add the tenderloin and brown well on all sides. Place in the oven and cook for 20 to 30 minutes or until cooked to an internal temperature of 160°F. Allow to rest for 5 minutes.
Prepare the Dijon Mustard Sauce: While the roast is cooking in the oven, stir the chicken stock and cornstarch together until the cornstarch is dissolved; stir in the mustard and milk. Pour into a small saucepan and bring to a simmer, cook until it has thickened. If you like a thicker sauce, add a bit more cornstarch that has been mixed with a bit of water. Taste and adjust for salt.
To Serve: Slice the tenderloin and spoon on the sauce.