For the pickled red onions: Combine the sugar, white vinegar, cider vinegar, salt, mustard seeds, red pepper flakes, celery seeds, turmeric, allspice, cloves and cinnamon in a medium saucepan and bring to a boil over medium-high heat. Pack the red onions into jars or place them in a nonreactive bowl and cover with hot pickling liquid. Cover and refrigerate overnight.
For the mole sauce: Stem and seed the ancho, guajillo and arbol chiles. Heat the oil in a large pot and fry the chiles to crisp and toast the skin. Remove the chiles and set aside. Add the cloves, garlic, cinnamon and onion to the pot and fry until brown. Remove and hold with the chiles. Add the bread, peanuts and sesame seeds and fry until brown. Return all the fried ingredients to the pot and stir in the chocolate. Transfer to a blender and puree, adding enough chicken stock to thin to a smooth paste. Season with salt.
Preheat the oven to 350 degrees F.
For the meatballs: With your fingers, mix together the pork, ricotta, salt, parsley, garlic, smoked paprika, sambal oelek and egg in a bowl. Take care not to knead the meat or overmix. When everything is incorporated, roll into 2 1/2-ounce balls.
Set the meatballs on a lightly oiled baking sheet and bake until cooked through, about 10 minutes.
Meanwhile, transfer the mole sauce to a saucepan and set over low heat to heat through.
Serve the meatballs topped with warm mole sauce and pickled red onions. Garnish with Cotija and cilantro.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.