Peel and chop the sweet potatoes into 2-inch cubes.
Add the sweet potatoes to a large pot in a steamer basket over 2 inches of water.
Cook for 20 minutes until sweet potatoes are tender.
In a small saucepan melt the butter and thyme on medium heat until just melted, then turn it off and let it sit.
Remove the sweet potatoes from the pot and drain the water.
Add the sweet potatoes, salt, pepper, and milk together.
Mash well with a potato masher or use an immersion blender to mash well.
Spoon sweet potatoes into a large serving bowl.
Pour the melted butter and thyme over the potatoes and serve.