Prepare the Oven and Muffin Tin:

• Preheat the oven to 350°F (175°C).
• Grease or line a 12-cup muffin tin with paper liners.

Dry Ingredients:

• In a large bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.

Wet Ingredients:

• In a separate bowl, beat the butter, granulated sugar, and brown sugar until creamy and smooth.
• Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.

Combine Wet and Dry Ingredients:

• Gradually add the dry ingredients to the wet ingredients, alternating with buttermilk. Mix until just combined.

Add Rhubarb:

• Gently fold in the chopped rhubarb until evenly distributed throughout the batter.

Fill Muffin Tin:

• Divide the batter evenly among the muffin cups. Sprinkle with coarse sugar, if desired, for a little extra crunch.

Bake:

• Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Cool and Serve:

• Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely. Enjoy!