Preheat the oven to 350°F with a center rack. Lightly spray and parchment-line an 8 1/2-by-4 1/2-inch metal loaf pan.
Spoon off only a separate clear pool of whey from the cottage cheese, then measure 1 cup without packing or pressing it dry.
Blend cottage cheese, salt and optional seasonings for 45 to 60 seconds until glossy and completely smooth. Set aside.
Mix cool water and egg white powder on low for 60 seconds. Scrape any dry pockets and let stand 2 minutes.
Add cream of tartar and whip on medium-high for 6 to 9 minutes, until glossy stiff peaks stand upright without looking dry or clumpy.
Stir one-quarter of the foam into the cottage cheese to lighten it. Gently fold that mixture into the remaining foam just until large streaks disappear.
Transfer batter immediately to the pan, mound it slightly in the center and smooth with only a few gentle strokes.
Bake undisturbed for 40 minutes, then check. Continue to 185°F to 190°F in the center for a firm slice, about 45 to 55 minutes total; tent if browning quickly.
Turn off the oven, crack the door and rest the loaf 10 minutes. Unmold, remove parchment and cool upright on a rack for at least 90 minutes before slicing.
