Add chopped sweet potatoes to slow cooker and cover and cook on low for 5-6 hours or on high for 2-3 hours.
With 30 minutes left, heat a large skillet over medium-high heat. Add bacon and cook until crispy, about 5-6 minutes. Drain the excess fat and transfer bacon to paper towel-lined plate.
Melt butter in same skillet and cook until starting to brown, about 2-3 minutes. Add garlic and sage and cook for 30 seconds. Remove from heat and set aside.
Using potato masher, mash sweet potatoes until desired consistency. Stir in browned butter, maple syrup, salt, pepper and bacon. Serve immediately.
Notes
You know the sweet potatoes are done when you can easily stick a fork or knife through the center of the potatoes.
If you don't want to use a pan, you can place bacon on parchment-lined baking sheet and bake at 400°F for 20 minutes.
You will know the brown butter is ready when there is a nutty aroma and there are lightly browned specks on the bottom of the pan.