Heat oven to 350°F (175°C). Line a baking sheet with parchment.
In a bowl, whisk oats, oat flour, baking soda, salt, and cinnamon.
In another bowl, whisk coconut sugar, maple syrup, egg, coconut oil, and vanilla until glossy and smooth.
Pour wet into dry and fold gently. If the mixture looks crumbly, add milk 1 tablespoon at a time until it forms a soft, scoopable dough.
Fold in dark chocolate chips (and nuts if using). Do not overmix unless you like tough cookies—no judgment, just… don't.
Pop the bowl in the fridge for 10–15 minutes for better shape and thicker cookies.
Use a 1.5-tablespoon scoop. Roll lightly and place 2 inches apart. Press each ball down slightly; oat cookies don't spread as much.
9–11 minutes until edges are set and centers are just barely soft. They'll continue to firm up as they cool.
Sprinkle with flaky salt while warm (optional but elite). Cool on the sheet 5 minutes, then transfer to a rack.
Warm is wildly good. Try not to “taste test” half the batch. FYI, no one succeeds at this step.