Crack the 4 eggs into a mixing bowl. Add the 280 g cottage cheese, salt, and pepper, and whisk with a fork until mostly combined. Small curds are fine.
If your cottage cheese looked watery in the carton, drain it in a fine-mesh sieve for 5 minutes before mixing it in step 1.
Drop the sourdough slices into the toaster and toast while the eggs cook, so they finish around the same time.
Melt the butter in a 10-inch nonstick skillet over low heat, tilting the pan so it coats the bottom.
Pour in the egg and cottage cheese mixture. Let it sit undisturbed for 30 seconds, then start pushing it gently with a rubber spatula from the edges toward the center.
Keep the heat low and keep folding gently, forming soft curds, for 4 to 5 minutes until the eggs are mostly set but still a little glossy on top.
Pull the skillet off the heat while the eggs still look slightly wet, they'll finish setting from carryover heat in the next minute.
Plate the toasted sourdough and spoon the eggs over the top. Sprinkle with chopped chives and serve right away.