Fry the bacon in a skillet and remove most of the fat – save it for browning the beef.
Add the onions and garlic to the bacon and cook for 3-4 minutes more until the bacon is crispy and the onions are soft. Scrape all this into the slow cooker.
Working in batches and using the remaining bacon fat – adding oil if you run out of fat – season the beef cubes and sear them in the fat. 2-3 minutes per side until nice and brown but not fully cooked. Put the beef into the slow cooker.
When you've finished searing the beef, toast the spices in the same skillet. Just put the spices in the skillet and stir them around over medium heat until fragrant.
Add 1/2 cup of beef stock to the skillet to deglaze the pan. Pour all of this into the slow cooker.
Add the remaining ingredients – the crushed tomatoes, beef broth, tomato paste, and any leftover pan juices or bacon fat to the slow cooker.
Cook on high for about 4 hours, or on low for 6.
When the meat is tender, season with salt and pepper and thicken with 1/4 tsp of xanthan gum and allow it to rest for 5 minutes before adding up to 1/4 tsp more.