For the cookies:
Heat the oven to 350 ℉ with the racks in upper and lower thirds.
On a rimmed baking sheet, spread the oats in a single layer. Bake on the lower rack, stirring once halfway through, until fragrant and lightly toasted, about 12 minutes. Transfer the pan to a wire rack; let the oats cool completely.

Meanwhile, place 5 tablespoons of the butter in a 1- to 2- quart saucepan. Cook over low heat, swirling the pan occasionally, until the butter has a nutty aroma, is a rich brown color, and the bottom of the pan is speckled with browned bits of the milk solids, 12 to 14 minutes. Transfer the brown butter to a small bowl and let cool for 20 minutes.

In a medium bowl, whisk together the cooled toasted oats, flour, baking powder, cinnamon, and salt. In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl with a hand mixer, beat the remaining 5 tablespoons soft butter and the brown sugar on medium-high until very smooth, about 2 minutes. Add the brown butter and continue beating on medium-high until light and fluffy, 3 to 5 minutes. Mix in the egg and beat thoroughly, scraping down the sides of the bowl if necessary, until incorporated. Beat in the vanilla. With the mixer on low, or by hand, mix in the dry ingredients until just combined. Fold in the dates, and walnuts if using.

Line two baking sheets with parchment paper. Form the dough into 24 balls (each about 2
tablespoons). Arrange the balls on the baking sheets, spacing at least 2 inches apart. Press
each ball into an even 2-inch round.
Bake 10 minutes for soft and chewy cookies. Remove from the oven and let cool for 1 to 2 minutes on the baking sheets. Using a spatula, transfer the cookies to a wire rack to cool completely.

To assemble the sandwiches:
Place 12 cookies flat side up on a clean work surface. Working quickly, place ⅓ cup ice cream
on each. Sandwich with remaining 12 cookies, flat sides together, and gently press to adhere.
Serve immediately, or wrap individually in plastic wrap and then in foil, and freeze for up to 3
days.

Adapted from "Bringing It Home: Favorite Recipes from a Life of Adventurous Eating” by Gail Simmons. Copyright © 2017 by Gail Simmons. Used with permission by Grand Central Publishing. All rights reserved.