Cardamom Orange Flourless Chocolate Cake

From Food 52.
Ingredients:
1/2 cup butter, room temperature
10 ounces bittersweet chocolate, melted and cooled
1 teaspoon ground cardamom
Zest of one orange
4 eggs
1/2 cup sugar

Preheat oven to 350. Melt chocolate in a double boiler and then set aside to cool.
Creme room temperature butter. Add sugar and mix until light and fluffy. Add eggs one at a time until well blended. Mix in the chocolate, cardamon and orange zest, just until combined.
Pour into a lightly buttered pan. Bake for 25-30 minutes, until set. Let cool for about 10 minutes before removing from pan.