In a skillet over medium-high heat, cook the chopped onion for 5-7 minutes, until translucent (or increase the time to about 20 minutes if you like them caramelized). Add the garlic and cook for a minute or less, until fragrant.
Add the ground beef. Cook for 8-10 minutes, breaking apart with a spatula, until browned.
Transfer the ground beef mixture into a slow cooker. Add remaining ingredients, except bay leaf, and stir until combined. Place the bay leaf into the middle, if using.
Cook for 6-8 hours on low or 3-4 hours on high. If you used a bay leaf, remove it before serving.