Preheat your oven to 400°F (200°C) and line a 12-cup muffin tin with paper liners.

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

In another bowl, mix sour cream, melted butter, eggs, and vanilla extract until smooth.

Pour wet ingredients into dry ingredients and stir until just combined.

Fold in finely diced rhubarb.

Spoon the batter into the muffin cups, filling each about two-thirds full, and sprinkle with topping.

Bake for 18–22 minutes or until golden brown and a toothpick comes out clean.

Let cool in the pan for 5–10 minutes before transferring to a wire rack.