Preheat the oven to 325 F.
Make the honey mustard: In a medium bowl, whisk together the honey, dijon mustard, and apple cider vinegar. While constantly whisking the dijon and honey mixture, slowly pour in the olive oil and whisk to combine.
Heat olive oil a large, oven-safe lidded pot over medium-high heat. Add the onions and whole garlic cloves and cook 3-4 minutes per side until browned and remove from the pan.
In a small bowl, combine the salt, pepper, and garlic powder. Season pork liberally with the salt mixture then brush with 1/3rd of the honey mustard dressing. Brown 5-6 minutes on one side, then flip. Add the onions and garlic back to the pan, along with the broth and thyme sprigs. Spoon another few scoops of honey mustard dressing back on top of the pork roast.
Place the lid on the pot and bake at 325 F until a thermometer inserted into the center of the pork registers 145 F, or about 1 hour.
Remove the roast from oven and let sit for 15 minutes before slicing, then serve with additional honey mustard dressing for dipping.