Whisk egg in large bowl. Add peanut butter and sugar and whisk until well blended and smooth. Scoop mounds of dough or roll balls and place on prepared baking sheets about 2” apart. Press lightly with fork to make criss-cross pattern.
Optional: Sprinkle lightly with flaky sea salt and sprinkle with chocolate chips.
Bake 8-10 minutes, until edges are set and cookies are slightly browning. Don’t overbake—these cookies are best if slightly underbaked.