Sprinkle flour in the slow cooker then add a couple of splashes of beef stock - just enough to get all of the flour wet. Whisk the flour to ensure it fully incorporates with the liquid. Then add a little more liquid, enough to make a slurry, and whisk again. This step will prevent the flour from becoming lumpy.
Add venison, sliced mushrooms, onion, garlic, tomato paste, Worchestershire sauce, rosemary, bay leaf, and fresh ground pepper to your slow cooker, along with the remaining beef stock.
Set slow cooker on high and let cook for 4 hours, or set on low heat for 6 hours.
15 minutes prior to serving add the gnocchi and shred the venison, if desired.
Ladle into bowls and serve with crusty bread to sop up the dark rich both.