Preheat your oven to 375ºF (190ºC). Gather your ingredients and set out your mixing bowls and baking sheets.

Cream the softened butter and brown sugar in a large mixing bowl until light and fluffy. Add in the egg and mix for about 2 minutes.

In a separate bowl, whisk together the flour, cinnamon, salt, baking soda, and baking powder.

Gradually add the dry mixture to the wet ingredients while mixing on low speed until just combined.

Gently fold in the finely diced rhubarb until evenly distributed.

Using a cookie scoop, portion the dough onto a greased baking sheet, spacing about 2 inches apart.

Bake for 12-14 minutes until the edges are lightly golden and the centers are set.

Cool on the baking sheet for about 5 minutes before transferring to a wire rack.