For the compound butter: To the bowl of a food processor, add the butter, Dijon, garlic, shallots, thyme, rosemary, parsley and salt and pepper to taste. Process until fully combined, then season with more salt, if needed. Lay out a large piece of plastic wrap. Place the compound butter in the center and roll the plastic wrap around it, twisting both ends so it is in the shape of a log. Place in the fridge to set until firm, at least 20 minutes. The compound butter will keep, tightly wrapped, in the refrigerator for up to 1 week and in the freezer for up to 1 month.
Meanwhile, preheat the oven to 420 degrees F.
For the smashed potatoes: Combine the olive oil and grated garlic in a small bowl and set aside. Place the potatoes in a medium saucepan and cover with cold water by 1 to 2 inches. Season the water generously with salt and bring to a boil over high heat. Reduce the heat and cook the potatoes at a low boil until fork tender, 20 to 25 minutes. Drain the potatoes and transfer a rimmed baking sheet. Using the bottom of a cup, gently smash the potatoes into patties. Drizzle with the garlic oil and bake until the skin is crispy, 8 to 10 minutes. When the potatoes are done, remove them from the oven and keep warm.
For the steak: Meanwhile, line a sheet pan with a rack and set aside. Season the steaks liberally with salt and pepper and drizzle with olive oil on both sides. Heat a large cast-iron skillet over medium-high heat. Add the steaks and cook, undisturbed, for 1 1/2 to 2 minutes. Flip the steaks and add the garlic, thyme, rosemary and butter. Using a sauce spoon, baste the steaks with the melted butter and aromatics and cook 1 1/2 to 2 minutes more. Transfer the steaks and aromatics to the prepared sheet pan and cook in the oven until the internal temperature registers 140 degrees F, 10 to 12 minutes.
Transfer them to a cutting board and allow to rest for at least 5 minutes. Remove the bone from each steak and slice the meat against the grain. Season to taste with salt.
Slice six 1/2-inch coins of compound butter. Plate the steak, top with the compound butter and serve with the smashed potatoes.