Remove the string from roast and cut into 3 or 4 equal pieces.
Lightly season roast pieces with salt and pepper.
Heat a heavy bottomed pan over medium-high heat.
Add oil to pan and brown the pork on all sides, in two batches if using a smaller pan.
Remove the pork and set aside.
Cool down the pan a bit, and sauté the onion and garlic over medium heat for about 2 minutes until softened a bit.
Deglaze the pan with a splash of wine.
Add the reserved pork, rosemary, bay leaf, and 1 ½ cups of wine to the pan; bring to a boil over high heat.
Turn down to simmer; cover and cook over med-low heat for 2 hours. Half way through the cooking time, flip the pork pieces over.
Remove the pork and set aside covered with foil to keep warm. Discard the bay leaf and the rosemary sprigs.
Increase the heat to high, add the tomato paste and the sugar, and reduce the liquid for about 10-15 minutes until syrupy.
Taste and adjust seasonings if needed.
Finish the sauce by removing from heat and stirring in butter until just melted.
Cut the pork into bite-sized pieces or slices.
Serve immediately; plate a mound of “Garlic Mashed Potatoes” in the center with a few pork pieces on top. Drizzle a couple tablespoons of sauce over the pork and on the plate around the mashed potatoes.
Garnish with freshly chopped parsley and a sprig of fresh rosemary.