Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.

In a large bowl, cream together the softened butter and packed brown sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

Gently fold in the finely chopped rhubarb and optional nuts.

Drop rounded tablespoons of dough onto the prepared baking sheets, about 2 inches apart.

Bake for 10-13 minutes, or until the edges are golden brown and the centers are set.

Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.

For the optional glaze: Whisk together powdered sugar and milk (starting with 1 tablespoon and adding more as needed) until smooth and drizzly. Drizzle over cooled cookies.