1. Preheat the oven to 325°F (163°C) to 350°F (177°C). Line a baking sheet with parchment paper.
2. In a large bowl, cream the softened butter and sugar together until light and fluffy.
3. Mix in the vanilla extract.
4. In a separate bowl, whisk together the all-purpose flour and salt.
5. Gradually add the flour mixture to the butter mixture, stirring until just combined.
6. Fold in the diced rhubarb gently, along with any optional nuts, zest, or spices if using.
7. Shape the dough into balls or form into a log. If using a log, chill in the refrigerator for at least 30 minutes before slicing.
8. Place cookie dough balls or sliced logs onto the prepared baking sheet, spacing them about 2 inches apart.
9. Bake for 15-25 minutes until edges are lightly golden and centers remain tender.
10. Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
11. Optional: Drizzle cooled cookies with powdered sugar glaze for added sweetness and presentation.