Line the bottom of a 9-inch (23 cm) springform pan with parchment paper and bottom and lightly grease the sides.
In a medium saucepan over medium-low heat, stir together butter and chocolate chips, ensuring chocolate doesn't burn, until just melted and blended.
Transfer chocolate mixture to a bowl. Using a wooden spoon, beat in sugar. One at a time, beat in eggs, mixing well after each addition. Sift in cocoa powder and stir until just blended. Pour into prepared pan.
Bake in center of preheated oven for 35 to 40 minutes or until cake has risen, has a thin crust and center is firm.
Transfer to a wire rack and let cool in pan for 10 minutes. Invert onto a platter. Remove pan sides and parchment paper. Let cool completely, then sift confectioners' sugar over top.
per serving: Calories 231, Carbohydrates 23 g, Sugars 18 g, Fructose trace, Glucose trace, Protein 4 g, Fat 17 g, Saturated Fat 10 g, Cholesterol 100 mg, Total Fiber 2 g, Calcium 41 mg, Iron 2 mg, Sodium 26 mg, Vitamin A 120 RAE, Vitamin C trace