Spray the inside of a large slow cooker with cooking spray
Heat a large saucepan on the stove-top over medium-high heat. Crumble in the buffalo meat and cook until well browned, about 7 to 8 minutes . Use a slotted spoon to transfer the meat to the slow cooker. Drain off half the fat in the saucepan and discard it. Add the onion and garlic to the remaining fat and saute until translucent, 6-8 minutes.
Pour the onion, garlic, and pan juices into the slow cooker. Ad the tomato sauce, tomatoes, Worcestershire sauce, chilli powder, cumin, oregano, brown sugar, cinnamon, all spice, cayenne, bay leaf, beer and tomato paste. Give it a stir and add the pinto beans. Cover and cook on low for t least 8 hours and up to 10 hours, skimming off any surface fat from time to time.
If you prefer a thicker chilli, during the last 45 to 60 minutes before serving. Mix together the fine cornflour and cold water in a small bowl. Then remove the lid, crank the slow cooker up to high, and whisk in the corn flour mixture.
During the last 15 minutes of cooking, season with salt and pepper.
Remove the bay leaf. Serve the chilli topped with the garnishes or pass them to the side.