First of the season kumquats (yum!) surfaced this morning at the Hamada Farms stand at the San Francisco Ferry Plaza Farmers Market.  I love the sweet skin and tart flesh of this citrus-y fruit.

In season, we keep a few out on the countertop so that we can just grab them for a treat when we walk by.  I also put kumquats into beet salads, use the zest to garnish fava beans and burrata, and make kumquat shortbread cookies.  One of my favorite ways to use kumquats, though, is in this dense upside-down cake.  I cook it in a cast iron skillet.

Ingredients
For bottom of pan:
1/2 stick butter (2 oz.)
¾ cup brown sugar
About two dozen ripe kumquats, washed and dried

For the cake:
1 stick butter (4 oz.), softened
1 cup brown sugar
3 eggs – 2 separated into yolks and whites
1 ½ cups unbleached all-purpose flour (plain)
1 teaspoon baking powder
¼ teaspoon salt
1/2 cup  orange juice
1 teaspoon vanilla extract

You will also need:
Iron skillet or 10″ baking pan
Paring knife
Cutting board
Mixing bowl
Electric mixer
Large spoon

Instructions
Preheat the oven to 350°F.

Cut 1/2 stick of butter into chunks and put them into an iron skillet. Melt over medium heat on top of the stove. When the butter has melted, add ¾ cup of brown sugar and stir over medium heat until bubbly. Remove from the heat and cool slightly.

Slice the kumquats crosswise into 1/4″ thick slices. Remove any seeds and discard them.  Place the kumquat slices on top of the butter and brown sugar mixture in a decorative pattern.

Using an electric mixer, beat a stick of butter at medium speed until it is smooth. Add a cup of brown sugar and mix for about 1 minute. Add the whole egg and 2 egg yolks and beat at medium speed for about 2 minutes.

Meanwhile, in a small bowl, mix together the flour, baking powder and salt. Add ½ of the flour mixture to the butter and sugar. Mix until just combined. Add half of the orange juice. Mix to combine. Repeat with the remaining flour mixture and juice. Mix to just combine the ingredients. Stir in the vanilla. The mixture will still be lumpy.

Beat the egg whites until they form soft peaks. Fold them into the batter.

Pour the batter on top of the kumquat slices in the skillet.

Bake for approximately 30-35 minutes until cake is set.

Remove from the oven and let cool for about 5 minutes. Run a knife around the side of the skillet to loosen the cake. Invert onto a serving platter.

Let cool and serve with a dollop of freshly-whipped cream or creme fraiche.

Serves 8.