Make the oat flour: Preheat the oven to 350°F (180°C) and line a large baking sheet with parchment paper.Add ½ cup of the rolled oats to a blender or food processor and blend into a fine flour. Transfer the oat flour to a large bowl.
Blend the wet ingredients: If the dates are firm, soak them in hot water for 10 minutes, then drain well.Add ½ cup of the dates, 1 large egg, ⅓ cup unsweetened applesauce, and 1 teaspoon vanilla extract to the blender or food processor. Blend until smooth and creamy, scraping down the sides as needed.
Make the dough: To the bowl with the oat flour, add the remaining 1½ cups rolled oats, 1 teaspoon cinnamon, ¼ teaspoon ground nutmeg, ½ teaspoon baking soda, ½ teaspoon baking powder, and ¼ teaspoon saltStir to combine.Pour in the blended date mixture and stir until no dry flour remains. Fold in the remaining ½ cup chopped dates.
Shape the cookies: Scoop about 2 tablespoons of dough and shape it into a cookie with your hands. If the dough is too wet, let it rest for 10 minutes. If it's sticky, lightly wet or oil your hands.Place the cookies on the prepared baking sheet about 2 inches apart. Since they won't spread much, this is their final shape.
Bake and cool: Bake at 350°F (180°C) for about 12 minutes, until the edges are lightly golden and the centers are set but still soft.Cool on the baking sheet for 5 minutes, then transfer the cookies to a wire rack. They will firm up as they cool.
Substitutions
Rolled oats → Quick oats (cookies will be softer).
Oat flour → Blend rolled oats into flour, whole wheat flour, or a gluten-free flour blend.
Medjool dates → Deglet Noor dates (soak first if firm).
Egg → Flax egg (1 tablespoon ground flaxseed mixed with 3 tablespoons water and let it thicken for 5 to 10 minutes before adding it to the dough).
Unsweetened applesauce → Olive oil or melted butter.
Vanilla, cinnamon, nutmeg → Pumpkin pie spice or cardamom.
Pecans or walnuts (optional) → Pumpkin seeds, sunflower seeds, or dark chocolate chips – 3 to 4 tablespoons.
Tips
Use soft dates: Soak firm dates in hot water for 10 minutes before blending if your dates are dry.
Wet your knife: It keeps sticky dates from clinging to the blade.
Flatten the cookies: They won't spread much as they bake.
Don't overbake: Pull them out when the edges are lightly golden.
Store well: Keep in an airtight container for 4 days, refrigerate for 1 week, or freeze for up to 3 months.