Rhubarb Upside-Down Muffins

Ingredients:
For the rhubarb:
1/4 cup (1/2 stick) unsalted butter
3/4 cup light brown sugar
1 tsp. oramge zest
1 pound fresh rhubarb, cut into 3/4 inch chunks
For the muffins:
1 1/2 cup all-purpose flour
1 tsp. baking powder
1/2 tsp baking soda
1/2 tsp salt
1/2 tsp ground cinnamon
1/8 tsp ground nutmeg
1/2 cup (1 stick)butter, softened
1/2 cup light brown sugar
1/4 cup granulated sugar
1 large egg
1 tsp pure vanilla extract
3/4 cup sour cream
2 tablespoons milk

Directions:
Preheat the oven to 375 degrees and grease a muffin tin.

To make the rhubarb topping:
Melt the butter in a saucepan over low heat. Stir in the brown sugar until dissolved. Stir in the orange zest over medium heat. Add the rhubarb, and cook over medium heat for 7 to 8 minutes. Remove the rhubarb from the pan with a slotted spoon,and let cool on a cookie sheet. Cook the remaining syrup until it is reduced to 1/2 cup, then pour into a glass measuring cup. Pour about 1 tsp. of syrup into each muffin cup, followed by the rhubarb.

To make the muffins:
Whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In a separte bowl, mix the butter with an electric mixer until fluffy and lightened in color. Gradually add the brown sugar, then add the granulated sugar. Beat in the egg and vanilla.
With a rubber spatula, fold in 1/2 of the flour mixture, followed by the sour cream. Fold in the remaining flour mixture and the milk.
Pour the batter over the rhubarb in each muffin cup. Bake for 23 to 25 minutes, rotating the pan halfway through. Remove the muffins from the oven, and let cool in the pan for about 5 minutes. Invert the pan onto a plate and let rest for another 5 minutes. Remove the pan and let the muffins cool.

Source:
Walter, Carole. Great Coffee cakes, Sticky Buns, Muffins, and More. New York: Clarkson Potter Publishers, 2007.