Cranberry Walnut Upside Down Cake

Ingredients

• 1.5 teaspoons double-acting baking powder 
• 1 teaspoon baking soda 
• 0.8 cup buttermilk well-shaken
• 1.8 cups cranberries fresh frozen thaw (7 ounces; do not if )
• 2 large eggs 
• 1.5 cups flour all-purpose
• 0.8 cup granulated sugar 
• 0.8 cup brown sugar light packed
• 8 servings accompaniment: lightly whipped cream sweetened
• 0.5 teaspoon salt 
• 0.5 cup butter unsalted softened
• 0.5 teaspoon vanilla 
• 3 ounces walnut pieces toasted coarsely chopped

Equipment

• bowl
• frying pan
• oven
• knife
• whisk
• plastic wrap
• hand mixer
• skewers

Directions

1. Melt butter in skillet over moderate heat, then swirl to coat bottom and side of skillet and stir in brown sugar. Simmer, stirring, until sugar is dissolved, 1 to 2 minutes, then sprinkle cranberries and walnuts evenly over butter mixture and remove from heat.
2. Put oven rack in middle position and preheat oven to 350°F.
3. Whisk together flour, baking powder, baking soda, and salt. Beat together butter and sugar in a large bowl with an electric mixer at high speed until light and fluffy, 4 to 6 minutes.
4. Add eggs, 1 at a time, beating well after each addition. Beat in vanilla. Reduce speed to low and add flour mixture alternately in batches with buttermilk, beginning and ending with flour mixture and mixing until just combined. (Do not overmix.)
5. Heat topping in skillet over moderately high heat until it starts to bubble, then gently spoon batter over topping and spread evenly. Quickly transfer to oven; bake until cake is golden brown and a wooden skewer comes out clean, 25 to 30 minutes. Cool cake in pan on a rack 15 minutes. Run a thin knife around inside edge of pan, then invert a serving plate over pan and invert cake onto plate. Cool completely on plate on rack, 1 hour.
6. Serve cake at room temperature.
7. Cake can be made 1 day ahead and kept, wrapped in plastic wrap, at room temperature.