Preheat oven to 350°F. Mix peanut butter and maple syrup together well until you have a thick cookie batter. Spread a sheet of parchment paper onto a cookie sheet and spoon out 10 equally sized cookies. Use fork tines to make hatch marks on the top of the cookies and sprinkle each with a pinch of flaky sea salt. Bake for 12–15 minutes, cool on the pan for 15–20 minutes, and serve.