Melt the butter/tallow in a large skillet over medium-high heat. Add the sliced onions and cook them until they are softened, for about 5 minutes. 

Add the liver strips to the skillet and cook them for about 5 minutes per side, or until browned, season with salt, pepper and garlic. 

Once everything is cooked through, add 1 tablespoon of the bone broth to the flour and mix until it forms a paste. 

Add this mixture to the rest of the bone broth, then add it to the skillet and bring it to a boil. 

Reduce the heat to low and simmer for 2-3 minutes, or until the sauce has thickened slightly. 

Serve immediately.