In a skillet, melt 1 tablespoon of butter and saute the onion until tender, but not brown. Set aside to cool.
In bowl, combine the cottage cheese, spinach, egg, feta and pepper. Stir in the sauteed onions.
Carefully cut the phyllo sheets in half lengthwise. COVER WITH PLASTIC WRAP, AND THEN COVER WITH A DAMP TOWEL that has been squeezed dry- you have to be very careful about not drying out the phyllo. Working with 1/2 sheets, fold in half lengthwise. Brush lightly with melted butter. Place 1 tablespoon spinach mixture in a corner. Fold up in a triangle to the end (like you're folding a flag). Trim the edges with scissors. Brush the outsides lightly with the remaining butter. Place on a baking sheet and cover with a damp towel.
Freeze until ready to bake. It's best to freeze these on a baking sheet. Once they're frozen, you can move them to a large zip bag or a freezer-safe container.
Bake (frozen) at 350 degrees for 25 minutes, or until golden. Serve warm.
Notes
This is a wonderful recipe to make ahead. Prepare a whole bunch of them to keep in the freezer and bake them up when you have guests over.