Place the bacon in a heavy-bottomed, 8" or so wide pot set over medium heat. Cook until the fat is rendered out and the bacon is slightly crispy. Now drain all but 1 Tbsp. of fat from the pot.
Add the onion to the pot and cook until very tender and lightly caramelized, about 10 minutes. Mix in the remaining ingredients, bring to a simmer, and cook 10 to 15 minutes, until the liquids reduce and the mixture slightly thickens and becomes jam-like.
Remove from the heat, transfer to a heatproof jar or serving bowl and cool to room temperature. Now cover and refrigerate until ready to serve. Bacon jam will keep several days in the refrigerator.
When ready to serve, serve as is or heat the jam 20 seconds or so in the microwave, which will melt any bacon fat on the surface and give the jam a nice shine.