1 cup (2 sticks) salted butter (you can sub unsalted)
2 1/4 cups dark brown sugar, packed
2 1/4 cups rolled oats
3 TBSP oat flour (you can sub all-purpose flour)
1 tsp salt
1 egg lightly beaten
2Â tsp vanilla extract
Flaky sea salt, for sprinkling (such as Maldon; optional)
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