How to Make It
Preheat the oven to 350°. Position racks in the upper and lower thirds of the oven. Line two baking sheets with parchment paper.
Combine the oats, oat flour, baking powder, baking soda and salt in a large bowl.
Beat the butter and sugars together in a large bowl with a mixer on medium to high speed until fluffy, about 4 minutes. Reduce the speed to low and beat in the egg, egg yolk and vanilla until smooth, about 2 more minutes. With a spatula, add the flour mixture, walnuts and dried apricots to the bowl and stir until fully combined.
Scoop the dough into 13 balls of about 1/3 cup each. Arrange the cookies 3 inches apart on the prepared baking sheets. Bake for 8 to 10 minutes, until the edges are golden and the centers are still very soft. Let cool 5 minutes on the baking sheets, and then transfer to wire racks to cool completely.
To make your own oat flour, put a few cups of rolled oats in a food processor or coffee grinder and pulse until a finely ground and powdery consistency is achieved.