Millet is a gluten-free grain commonly consumed in Asia and Africa. In the United States, however, it is not so common. It is high in vitamins and minerals and can be used in place of potatoes as a starch, as in this dish.
Using a grain mill or a high-powered blender, crack the millet just enough to expose the starchy center.
Combine the millet with the sourdough starter or kefir and 2 cups of water in a quart jar. Stir to combine, then place a clean towel or coffee filter over the jar and tighten a canning ring over it.
Place in a warm spot for 12 to 24 hours or until it smells just a bit sour.
When ready to cook, add the olive oil and minced garlic to a small pan. Sauté over medium heat for just a few minutes, then add remaining 1 cup of water and soured millet, salt, and pepper. Cover pan and bring to a simmer.
Turn heat to low and simmer until tender, about 30 minutes.
Remove lid, stir in milk and butter, and mash and stir until desired consistency is achieved. Taste and adjust salt and pepper as needed.