For the tomato sauce:
2 (28-ounce) cans whole tomatoes in juice
1/4 cup olive oil
1 medium sweet yellow onion, finely chopped
5 garlic cloves, minced
1 teaspoon sugar
1/2 California bay leaf
For the meatballs:
3 cups coarse fresh bread crumbs (6 slices white sandwich bread)
2/3 cup whole milk
1 pound ground pork
1 pound ground beef (not lean)
4 garlic cloves, minced
1 1/2 cups grated Parmesan
2 large eggs, lightly beaten
1/2 cup flat-leaf parsley, finely chopped
1/2 teaspoon dried oregano
1/2 teaspoon dried marjoram
2 cups vegetable oil
20 small (2-inch) slider buns, split
Optional: baby greens for garnish
To make the tomato sauce:
Purée tomatoes with their juice in a blender and transfer to a bowl.
Heat oil in a large heavy pot over medium-high heat and sauté onion until golden, about 6 minutes. Add garlic and sauté, stirring, 1 minute. Add tomato purée, sugar, bay leaf, and 1 1/2 teaspoons salt and simmer, uncovered, stirring occasionally, until thickened, 40 to 50 minutes. Discard bay leaf.
Make meatballs while sauce simmers:
Stir together bread crumbs and milk in a large bowl and let stand 10 minutes. Add meat, garlic, cheese, eggs, parsley, oregano, marjoram, 1/2 teaspoon salt, and 1/2 teaspoon pepper and blend until just combined well (do not overmix). Form level 1/4-cup portions into meatballs.
Heat oil in a 10-inch heavy skillet over medium-high heat hot and fry meatballs, about 6 at a time, turning occasionally, until well browned and cooked through, 4 to 6 minutes per batch. Transfer to paper towels with a slotted spoon.
Simmer meatballs in sauce and assemble sliders:
Add drained meatballs to tomato sauce and simmer, stirring occasionally, until meatballs are heated through.
Assemble sliders with a meatball and 1 tablespoon sauce per bun. Garnish with baby greens and secure each with a wooden pick.