Begin making the chiles: Heat oil in a large Dutch oven over medium; add onion, and cook, stirring constantly, until softened but not browned, 1 to 2 minutes. Add pork and beef; cook, stirring often to crumble into small pieces, until browned, 2 to 3 minutes. Add tomatoes and salt; cook, stirring often, until meat is cooked through, 12 to 15 minutes. Reduce heat to medium-low; add apple, pear, and plantain. Cook, stirring often, until fruit is softened, about 5 minutes.

Add almonds, candied pineapple, raisins, canela, and cloves to meat mixture; cook over medium-low, stirring occasionally, until juices in pan evaporate, 3 to 4 minutes. Remove from heat, and transfer mixture to a large bowl; let stand at room temperature, stirring occasionally, until just warm to the touch, about 1 hour.

Preheat oven to broil with rack about 6 inches from heat. Cut a 1-inch-long slit lengthwise along each poblano, starting at tip of chile. Place chiles on an aluminum foil–lined baking sheet; broil until blistered and slightly softened, 8 to 12 minutes, flipping halfway through cooking time.

Place poblanos in a large bowl; cover tightly with plastic wrap, and let stand 10 minutes. Peel poblanos to remove as much skin as possible. Insert a knife in the previously cut slit near the tip of the poblano, and cut lengthwise to split each chile open from tip to stem; remove and discard seeds. Set aside.

Make the walnut sauce: Combine queso fresco, cream cheese, walnuts, milk, almonds, crema, sherry (if using), sugar, salt, and white pepper in a blender; process until smooth, 1 to 2 minutes, stopping occasionally to scrape down sides.

Finish making the chiles: Stuff poblanos evenly with meat mixture (about ½ cup each), and place on a serving platter. Pour walnut sauce evenly over poblanos. Season to taste with salt. Garnish with pomegranate arils and chopped parsley.