1. Melt butter in a medium-sized saute pan on medium-high heat. Stir constantly and allow butter to brown slightly, but not burn.
2. Lower the heat and add garlic. Stir to prevent burning. When garlic starts to turn golden brown, add sage. Continue to cook for another 1 to 2 minutes, until the sage is fragrant.
3. Turn off the heat. Add lemon zest and mix.
4. In a 6-quart slow cooker, add Brussels sprouts, butter-garlic mixture, salt and pepper. Mix well.
5. Cook on high for 2 hours.
6. Add lemon juice and mix.
Serve with feta cheese sprinkled on top.
