Servings: one 1-cup jar

3 Tbs extra-virgin olive oil 3 Tbs extra-virgin olive oil
1-1/4 pounds onions (2 large), halved and sliced thin through the root end 1-¼ pounds onions (2 large), halved and sliced thin through the root end
1 bay leaf 1 bay leaf
1/2 tsp minced fresh rosemary ½ tsp minced fresh rosemary
1/2 tsp salt ½ tsp salt
1/4 tsp pepper ¼ tsp pepper
2 garlic cloves, peeled and mashed 2 garlic cloves, peeled and mashed
1/4 cup balsamic vinegar ¼ cup balsamic vinegar
1/4 cup water ¼ cup water
2 Tbs sugar 2 Tbs sugar

Heat oil in Dutch oven over medium-high heat until shimmering. Stir in onions, bay leaf, rosemary, salt, and pepper. Cover and cook, stirring occasionally, until onions have softened and released their liquid, about 10 minutes.
Stir in garlic. Reduce heat to medium-low and cook uncovered, scraping up browned bits, until onions are golden brown, about 15 minutes.
Stir in vinegar, water, and sugar, scraping up any browned bits. Increase heat to medium-high and simmer until mixture is thickened and rubber spatula or wooden spoon leaves distinct trail when dragged across bottom of pot, about 2 minutes.
Discard bay leaf. Transfer onion mixture to food processor and pulse to jam-like consistency, about 5 pulses; let cool slightly.
Using funnel and spoon, portion jam into one 1-cup jar. Let cool to room temperature and serve. (Jam can be refrigerated for up to 4 days; it must be discarded after 4 days.

Doubling note:  Doubling note:
Double all ingredients. Increase onion cooking time to 35 minutes in step 2, and jam simmering time to 10 minutes in step 3.  Double all ingredients. Increase onion cooking time to 35 minutes in step 2, and jam simmering time to 10 minutes in step 3.