Preheat oven to 425 degrees F. Brush bell pepper with grapeseed oil (reserving the rest of the oil) and roast in oven until charred, about 15 minutes. Remove from oven and place in a covered container or a plastic bag to sweat. Allow oven heat to drop to 350 degrees F.
Season short ribs with salt and pepper. Heat remaining 2 tablespoons of grapeseed oil in a large saute pan with a lid. Sear short ribs on all sides and remove to a utility platter. In the same pan, saute celery, carrots, and onion until the onion turns translucent. Add beef stock, tomato paste, molasses, rosemary, and thyme, and stir to combine. Return short ribs to pan, cover with a lid or foil and braise at 350 degrees F until the meat falls from the bone, about 1 to 1 1/2 hours.
While the short ribs are braising, peel the roasted bell pepper and cut julienne.
Remember to use an oven mitt when you remove the pan from the oven.
Remove rib meat and bones to a utility platter. Strain the pan juices into a bowl and then return them to the pan over medium-high heat. Create a slurry by whisking 2 tablespoons water into a small bowl of the cornstarch. Whisk the slurry into the pan juices and allow the mixture to thicken.
Arrange rib meat on a platter and spoon sauce over. Garnish with julienned roasted peppers, and sprinkle with parsley leaves.