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

Cream together ½ cup of softened unsalted butter and 1 cup of brown sugar until smooth and fluffy.

Beat in one large egg and 1 teaspoon of vanilla extract until fully incorporated.

Whisk together 1 and ½ cups of all-purpose flour, 1 teaspoon of baking soda, and ½ teaspoon of salt in a separate bowl.

Gradually mix the dry ingredients into the wet mixture until just combined.

Fold in 1 cup of diced fresh rhubarb carefully.

Drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes until edges are golden and centers look set.

Allow cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack.

Transfer cookies to a wire rack to cool completely.