1. In a thick-bottomed skillet over medium heat, sauté chopped onions in a small amount of cooking oil along with a pinch of salt (the salt helps to release the onions sweet juices). Cook uncovered, stirring occasionally until the onions are deeply golden, brown, and caramelized (about 15-20 minutes). Remove from heat and set aside to cool.
2. Meanwhile, preheat oven to 400°F. Line baking pan with parchment paper.
3. In a medium bowl mix chopped mushrooms with oil. Layer mushrooms evenly on prepared baking pan.
4. Bake for 15 to 20 minutes, stirring every 5-7 minutes, until the mushrooms are tender and reduced in size. Remove from the heat and allow to cool. Process in a food processor until finely chopped but not puréed. Set aside.
5. Turn oven temperature down to 375°F. Line a baking sheet with parchment paper.
6. In a small bowl, or mortar and pestle, combine spices.
7. In large bowl, lightly beat egg. Add cooled onions, roasted mushrooms, spice mixture and tomato paste. Stir until blended. Add ground beef, stir until combined.
8. Form into meatballs about 1 1/2 inches in diameter and place on prepared pan. Recipe makes about 24 meatballs.
9. Bake for 20 minutes, or until meatballs are nicely browned and cooked through. For even cooking, spin the pan after 10 minutes.
10. While the meatballs are cooking, make the sauce.
1. In a small saucepan, combine syrup, mustard, oil and vinegar, whisk to blend. Bring to a boil, reduce heat to low and simmer, stirring often, for 8 to 10 minutes or until reduced to a glaze-like consistency. Remove from heat.
Note: Be careful when stirring, as the hot liquid bubbles up, sputters and splashes.
1. Once finished cooking, arrange meatballs on a serving plate, top each one with a dollop of sauce, insert fancy toothpicks, sprinkle plated meatballs with chopped fresh rosemary, and serve warm, as appetizers.