Preheat oven to 350 degrees. Prepare roast by cutting small 1 inch deep slits into the meat. Fill slits with julienned garlic pieces. Rub entire roast with olive oil, salt, pepper, thyme, and rosemary (if applicable). Place into a roasting pan (or large baking dish) and bake 1 hour.
While roast is baking, melt butter and chicken stock together and finish preparing potatoes if you have not yet done so.
After an hour of baking, remove the roast. Pour about 1/4 cup of warm butter liquid onto the roast and around the pan. Shingle potatoes around the roast to create two layers of potatoes. Sprinkle on a few diced onions and pour on more butter liquid. Repeat this process until all ingredients are layered around the pork roast. Sprinkle paprika and parsley over the whole thing.
Return to oven and bake 45 minutes to an hour more. The dish is done once the potatoes are soft and the roast is cooked. Remove from oven and place roast onto a separate place to rest. Cover with foil and set aside.
Keeping the potatoes in the roasting pan, stir to coat potatoes in the gravy. If it seems too runny, keep stirring. The starch from the potatoes will thicken the sauce. Taste potatoes and adjust seasonings accordingly.
After 10 minutes, slice the pork loin roast thinly and serve with potatoes.