Sprinkle the beef liberally with the salt on all sides.
Rub the beef evenly with the mustard.
Pat the minced garlic and rosemary all over the beef.
When the smoker is ready, add the wood chunks over the coals and place the beef over the cooler side of the grill.
Cover and cook the beef until it reaches an internal temp of 120 degrees.
Remove from heat.
Sear the Beef
You can add more coals to the fire and get it going for a hot fire now, or use a stovetop for the next step.
Place a cast-iron skillet over the medium-high heat and melt 2 tablespoons of the butter. Swirl to coat the pan.
Quickly sear the beef on all sides, 3 to 5 minutes per side, for a good crust over the herbs and garlic.
Place the beef over heavy foil. Top with the two remaining tablespoons of butter and wrap it tightly.
Let the beef rest for 10 minutes, to an internal temp of 135 degrees, before slicing thin to serve.
Garnish with fresh rosemary and serve the smoked horseradish sauce on the side.
Make the smoked horseradish cream sauce:
Place a small heatproof pan with the heavy cream in it over the grate. Allow it to sit over the heat, without simmering for about 45 minutes to an hour.
Stir often. Taste a bit of the cream to make sure it has thickened a bit and has a gentle smoked flavor.
Remove from heat.
Melt butter in a cast-iron skillet over the fire.
Add the minced shallots and cook until crisp, 3 to 5 minutes.
Remove from heat.
In a bowl, whisk the mayo, mustard, sour cream, shallots and horseradish together.
Whisk in the smoked cream a little at a time until smooth and drips form a spoon but is still thick.
Season with black pepper and salt.
Garnish with fresh rosemary minced, if desired.
Notes
You want to make sure the smoker is prepped and holding temp before adding your wood. Depending on the smoker, I let mine pre-heat up to an hour before actually smoking the meat. Between getting good embers and a stable temp, these things can take time and always depend on the weather (wind, temp, altitude, etc). If you don’t have a chimney to light your coals, using small firestarters strategically placed in the pile of coals is a great way to light your fire. I build a pile of charcoal to one side of my smoker and nestle a firestarter or two in with a few chunks on top. Using a long lighter, I then light them and let the charcoal heat up and get ashen before even starting to cook. For this recipe, I smoked the wood with Western Wood Hickory Chunks. I am loving their chunks because they are the perfect size for a good smoke without building a fire that lasts all afternoon. And the wood is kiln-dried, meaning it burns clean with flavorful smoke in my smoker. It really has been great to work with.