Servings: 6 or 12

For the muffins: subheading: For the muffins:
9 oz. (2 cups) all-purpose flour 9 oz. (2 cups) all-purpose flour
3/4 cup granulated sugar ¾ cup granulated sugar
2-1/2 tsp. baking powder 2-½ tsp. baking powder
1 tsp. ground cinnamon 1 tsp. ground cinnamon
1/2 tsp. baking soda ½ tsp. baking soda
1/2 tsp. kosher salt ½ tsp. kosher salt
1 cup sour dough discard (OR 1/2 cup discard and 1/2 cup sour cream) 1 cup sour dough discard (OR ½ cup discard and ½ cup sour cream)
4 oz. (8 Tbs.) unsalted butter, melted and cooled slightly 4 oz. (8 Tbs.) unsalted butter, melted and cooled slightly
2 large eggs 2 large eggs
1 tsp. pure vanilla extract 1 tsp. pure vanilla extract
1-1/2 cups 1/4-inch-diced rhubarb (7-1/4 oz.) - I like to use frozen. 1-½ cups ¼-inch-diced rhubarb (7-¼ oz.) - I like to use frozen.
 
For the topping: subheading: For the topping:
3 Tbs. granulated sugar 3 Tbs. granulated sugar
1/2 tsp. ground cinnamon ½ tsp. ground cinnamon

Position a rack in the center of the oven and heat the oven to 400°F. Spray a 12-cup muffin tin with non-stick spray or line with paper or foil baking cups. For larger muffins, use a 6-cup muffin tin and increase baking time by 5 minutes.
Make the muffin batter: subheading: Make the muffin batter:
In a large mixing bowl, combine the flour, sugar, baking powder, cinnamon, baking soda, and salt and whisk to blend. Stir in the rhubarb pieces to coat.
In a medium bowl, whisk together the sourdough discard (or sour cream), melted butter, eggs, and vanilla until smooth. Lightly stir the sourdough mixture into the dry ingredients with a spatula until the batter just comes together; do not overmix. The batter will be thick.
Divide the batter among the muffin cups, using the back of a spoon or a small spatula to settle the batter into the cups. The batter should mound a bit higher than the tops of the cups.
Make the topping: subheading: Make the topping:
In a small bowl, combine the sugar and cinnamon and mix well. Sprinkle a generous ½ tsp. of the cinnamon-sugar mixture over each muffin.
Bake the muffins until they’re golden brown, spring back most of the way when gently pressed, and a pick inserted in the center comes out clean, 18 to 22 minutes. Transfer to a rack and let the muffins cool in the pan for 5 to 10 minutes. Carefully lift the muffins out of the pan-if necessary, loosen them with the tip of a paring knife-and let them cool somewhat. Serve warm.