Preheat the oven to 350 degrees F.
In a small bowl, mix together the rosemary, sage, garlic, 1 tablespoon of the olive oil and some salt and pepper. Score the pork belly and rub it with the herb mixture. Place the pork in a baking dish, add the beer, cover with foil, and cook for 3 hours. Set aside to cool, then roughly chop the pork belly.
While the pork is cooking, bring a large pot of water to a boil. Add the collards; cook for 3 minutes, then drain and rinse in cold water to stop cooking. Squeeze the greens by hand to remove excess water. Set aside.
In a separate pot, bring 6 or 7 cups of water and the remaining 2 tablespoons olive oil to a boil. Reduce the heat to a gentle simmer and slowly pour in the polenta. Cook for a couple minutes, stirring continuously. When the polenta begins to thicken, stir in the collard greens, pork and parsley and mix well; the finished polenta should be fairly loose. Serve.