• Preheat oven to 375°F. Line a standard muffin pan with paper liners.

Crumb Topping

• Create the crumb topping first. In a small bowl, use a fork to combine the flour, sugar, cinnamon, and salt. Add melted butter and mix with fork until crumbs form. Place bowl in fridge to chill while you make the muffin batter.

Rhubarb Muffins

• In a large bowl, whisk together the flour, sugar, baking powder, cinnamon, salt, and orange zest.
• In a medium bowl, whisk together the melted butter, egg, buttermilk, and vanilla. It's ok if it looks curdled/lumpy.
• Add the wet ingredients to the dry, and stir just to bring the batter together - do not overmix. It will be somewhat thick and lumpy.
• Fold in 1½ cups chopped (½" pieces) rhubarb, just enough to evenly distribute the rhubarb throughout the batter.
• Use a large 3-tablespoon scoop to portion batter evenly between the 12 lined muffin cups. If needed, fold the batter partway through, to redistribute rhubarb evenly throughout the batter again.
• Sprinkle tops of muffin batter with ¼ cup small-diced (¼" pieces) rhubarb pieces, and press them in very slightly.
• Remove crumb topping from fridge and use your fingers to break up any large pieces while sprinkling the topping evenly over the muffin batter.
• Bake for about 25 minutes, or until crumbs are golden brown. A toothpick should come out clean from the center of the muffins, and muffins should spring back when you gently press the top center of a muffin with your fingertip.
• Remove muffin pan from oven and let rest 5 minutes. Then remove muffins from the pan and let cool on a baking rack. Enjoy warm right away or let them cool first - just know that the crumb topping will have the best crispy texture on the day they're made.