Cut the beef and the pork belly into 1-inch pieces. Mix the salt with Cure #1. Place the meat and the pork belly in a bowl, sprinkle with the kosher salt and cure #1 mix, and mix well. Cover and cure in a refrigerator for 24-48 hours.
Take the meat out of the fridge, sprinkle with the mustard powder, onion powder, garlic powder, and black pepper, and mix well.
Pack the seasoned meat (not very tightly) into 16-oz wide-mouth mason jars, leaving 1/2" headspace, adding one bay leaf per jar.
Wipe the rims, place the lids on top and screw on the bands finger-tight.
Process at 250F (15 PSI) in a pressure canner for 70 minutes (see notes 1 and 2).
Remove the canner from heat and let it depressurize naturally.
Using a jar lifter, carefully remove the jars and place them on a towel or a cooling rack to cool down to room temperature for about 12 hours.
Remove the bands. Wipe the jars with a damp towel or paper towels. Test the seals.
Store in a cool, dark, and dry place for up to 2-3 years. The most optimal storage temperature is about 35F-59F (2C-15C).