Melt the bacon grease in a cast-iron Dutch oven over medium-high heat. If using bacon, slice into 1" pieces and fry until the fat has rendered. Remove the bacon from the pan, but leave the bacon grease, and add the onions.
Reduce heat to medium and saute the onions, stirring almost constantly, until clear. About 5 minutes.
Add the garlic and stir until aromatic, about 2 minutes.
Add the chili powder, paprika, cumin and lemon zest. Stir to combine all the ingredients and simmer together for about 2 minutes.
Add the chopped chipotle pepper, cranberries, and a pinch of salt. Stir completely to mix all ingredients.
Add the vinegar, lemon juice, and brown sugar. Stir well for a couple of minutes, until all the ingredients are combined.
Lower the heat to a simmer and cover for about 15 minutes while the cranberries break down. Stir occasionally.
Remove the Dutch oven from the heat and set aside for 5 minutes.
Pour the cranberry mixture into a blender and blend on high until pureed. The sauce will have a thick, paste-like consistency at this point. (see Notes)
Press the cranberry paste through a kitchen strainer. Remember to scrape off the bottom of the strainer and return the processed cranberry sauce to the Dutch oven. (see Notes)
Place the dutch oven over medium-high heat and mix in the beef stock, starting with about 1 cup. Stir or whisk to blend together, adding more stock until you reach your desired consistency. Bring the sauce to a high simmer for 5 minutes.
Reduce to a low simmer, cover and allow it to simmer for about 15 minutes, stirring frequently. Add more beef stock to thin out the sauce, if desired. (If you need it to thicken, just simmer without the cover)
Turn heat off and allow to sit for about 10 minutes.
Notes
Fry bacon cut into 1 " slices to render the fat or use bacon grease reserved from another recipe.Fresh or frozen cranberries are very tart, but the amount of brown sugar can be adjusted to your taste.Canned cranberry sauce can be substituted for the whole cranberries-use one 15-ounce can. There are other ingredients in the canned sauce, so you should consider the amount of brown sugar you use. Start with 1 cup, then add more after tasting, if desired.This recipe was developed using about ¼ ounce of chipotle pepper in adobo sauce-that was 1 pepper. To increase the spice (heat), add more.A blender and kitchen strainer works well to process the sauce. Optionally an immersion blender and a food mill will work as well. The final consistency of the sauce will depend upon the amount of beef stock or beef broth you add. You may use more than two cups of stock to get the consistency you like....that's OK!Chicken stock, vegetable stock, cranberry juice, or water can be substituted for beef stock. To make this vegetarian, substitute olive oil or vegetable oil for the bacon grease and vegetable stock for the beef stock.