MAKE MEATBALLS: Adjust oven racks to upper-middle and lower middle positions and heat oven to 450 degrees F.
Using fork, mash bread, milk, and egg yolks in large bowl until smooth.
Add pork, parsley, garlic, salt, and pepper and mix until incorporated. Add beef and knead gently until combined.
BAKE MEATBALLS: Form mixture into 1 1/4 inch meatballs (you should have about 80). Bake meatballs on 2 rimmed baking sheets until cooked through and beginning to brown, 12 to 15 minutes, switching and rotating sheets halfway through cooking.
Let cool to room temperature, then refrigerate until firm, about 30 minutes.
Transfer to large zipper lock freezer bag and freeze for up to 1 month.
MAKE SAUCE: Heat oil in Dutch oven over medium high heat until shimmering. Cook onion until softened, about 5 minutes.
Whisk in tomato sauce, preserves, sugar, Worcestershire, mustard, and epper flakes and bring to boil.
Reduce heat to medium-low and simmer until sauce is thickened, about 15 minutes.
Let cool to room temperature. Transfer to airtight container and freeze for up to 1 month.
TO SERVE: Reheat sauce, covered and stirring occasionally, in Dutch oven
over medium low heat. Once sauce reaches simmer, stir in frozen
meatballs and cook until heated through, 10 to 15 minutes. Serve.