In a heavy bottomed pot over medium high heat add butter, then onion and garlic, saute for 10 minutes.
Add brussels sprouts then season lightly with salt and pepper, cook stirring often for 5 minutes.
Add stock, cover and cook 5 minutes, remove cover then allow stock to evaporate by 75%
Add cream, spices and sage, stir and reduce cream by roughly half.
Adjust seasoning, enjoy.