Combine water, salt, and butter in a small saucepan and bring to a boil. Once it reaches the boil turn off heat and cover. Meanwhile, beat egg in a medium bowl and add kasha. Mix together until grains are thoroughly and evenly coated. Transfer to a medium-size, wide, heavy saucepan (I use Analon nonstick), place over high heat and stir egg-coated kasha constantly until grains are dry, smell toasty, and no egg is visible, 2 to 3 minutes. Add just-boiled water, turn heat to very low, cover and simmer 10 to 12 minutes for cracked kasha, 30 minutes for whole kasha, or until all of the liquid is absorbed. Remove from heat. Remove lid from pan, place clean dish towel over pan (not touching the grains), and cover tightly. Let sit undisturbed for 10 to 15 minutes. Fluff and serve.