Preheat the oven to 350 degrees Fahrenheit. Grease an eight-inch square pan.

Place the chocolate chips in a microwave-safe bowl. Microwave on high for about two minutes, stirring every 20 seconds after the first minute, until the chocolate is melted and smooth. If you have a powerful microwave, reduce the power to 50 percent.

Combine the beans and eggs in the bowl of a food processor fitted with the metal “S” blade. Process until smooth. Add the sugar, oil, cocoa, vanilla, and baking powder, and pulse to blend. Pour in the melted chocolate and blend until smooth, scraping down the corners to make sure the chocolate is completely mixed.

Transfer the batter to the prepared cake pan. Sprinkle with walnuts, mixing gently to incorporate. Bake in the center of the preheated oven for 40 minutes or until a toothpick inserted in the center of the cake comes out clean. Remove the pan to a rack to cool for 10 to 15 minutes. Invert the pan onto a serving plate. Remove the pan. Dust with confectioners’ sugar just before serving.