1. Place garlic, sage, and thyme in a piece of cheesecloth; tie with kitchen twine to enclose. Place in a medium saucepan along with celery root and enough milk to cover (you may not need to use all the milk). Bring to a simmer over medium heat; continue simmering until celery root is tender, 20 to 30 minutes. Strain mixture through a fine mesh sieve set over a medium bowl, reserving 1/2 cup of milk and discarding cheesecloth bundle.

2. In a small saucepan, melt butter over medium-high heat until nut-brown in color, about 8 minutes. Remove pan from heat and pour butter into a bowl, leaving any burned sediment behind.

3. Transfer one-third of the celery root, reserved milk, and browned butter to the jar of a blender; blend until smooth. Slightly mash remaining celery root with a wooden spoon or a potato masher. Stir in pureed celery root mixture and chives; season with salt and pepper. Serve immediately.