To make the poblano creme fraiche:
Combine the heavy cream and buttermilk in a plastic bottle or mason jar. Shake well for 10 seconds. Let sit at room temperature overnight. The next day the mixture will be thickened.
Place the poblano on the grill over direct high heat. Blacken on all sides. Place in a zip-top bag and allow to steam for 15 minutes. Remove from the bag. Remove the seeds and stem. Peel the skin off. Mince the remaining flesh.
Place the creme fraiche in a bowl. Add the minced poblano, garlic and lime juice. Season with salt and pepper. Mix well.
To make the strip loin:
Preheat your Yoder Smokers YS640 pellet grill to 250ºF set up for indirect grilling, with GrillGrates. Rub the surface of the loin with a thin layer of vegetable oil. Season with R Butts R Smokin’ R Beef Rub. Allow the rub to attach, resting the meat for 5-10 minutes.
Smoke the loin on the second shelf until the internal temperature reaches 105ºF. Remove the loin from the cooker and cover loosely with foil. Turn the cooker up to 450ºF. Using heat resistant leather BBQ gloves, move the GrillGrates aside. Remove the door from your two door diffuser (or the entire diffuser), and return the GrillGrates to their place over the fire box.
After about 5 minutes, the grill will have come up to temp. Place the loin on the GrillGrates. Grill on both sides to achieve nice grill marks, cooking until internal temperature reaches 125ºF. Pull, rest 10 minutes, slice to serve. Serve with the Poblano Creme Fraiche.