Chop bacon into 3/4 inch pieces. Thinly slice the onions & shallot. Set a large Dutch oven or heavy skillet over medium-high to high heat. Add the bacon and cook, stirring occasionally, until it begins to brown and crisp, 15 to 20 minutes. Keep all the bacon fat in the pan; do not discard (see note below).

Lower the heat to medium. Stir in the onions and shallots, and cook until softened, 8 to 10 minutes. Add the maple syrup, vinegar, Dijon, and Worcestershire sauce. Season with salt and pepper.

Pour in 1/2 cup of water and stir to combine. Bring the mixture to a boil, reduce heat to low and simmer, stirring occasionally if necessary. Cook until the the jam has a glossy appearance and syrup-like consistency, about 1 hour.

Allow the mixture to cool for 20 to 30 minutes. Transfer to a blender and pulse a few times to puree the larger pieces, stopping every pulse or two to stir and check the consistency — it should be thick and chunky, not a paste.

Transfer to an airtight container. Bacon jam can be refrigerated for up to one month (if it lasts that long). You can also can this to preserve it a bit longer if you prefer (it never lasts that long at my house). Serve at room temperature.

Note - Some people prefer to discard some of the bacon fat before adding the onions. I kept all of the fat because I used a lean bacon but it is personal preference. If you are using a more fatty bacon, then you may want to drain it and then add back whatever you feel you need when simmering or blending to get the right consistency you like.