Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Cream together the softened unsalted butter and brown sugar until light and fluffy, about 3-4 minutes.

Beat in the eggs one at a time, then add the vanilla extract and blend until smooth.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add to the butter mixture, stirring until just combined.

Fold in the diced fresh rhubarb until evenly distributed.

Scoop the dough onto the prepared baking sheet, leaving about 2 inches of space between each mound.

Bake for 12-15 minutes, until the edges are golden brown and the centers remain soft.

Let the cookies cool on the baking sheet for 2-3 minutes before transferring to a wire rack to cool completely.