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Preheat your oven to 350°F. Lightly grease a 9" square pan.
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To make the brownies: Combine the zucchini, melted butter, eggs, and vanilla in the work bowl of a food processor, and process until smooth.
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Add the sugar, cocoa powder, espresso powder, baking powder, salt, and flour; process briefly, just until well combined.
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Add the chips, and pulse several times, to break up the chips just a bit.
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Pour the batter into the prepared pan.
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Bake the brownies for 25 to 30 minutes, until a toothpick inserted into the center comes out clean, or with a few moist crumbs clinging to it; you shouldn't see any sign of wet batter. Remove the brownies from the oven, and allow them to cool completely before frosting.
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To make the frosting: Combine the chocolate chips and milk or cream in a microwave-safe bowl or small saucepan. Heat until the milk is steaming, and the chips are soft. Remove from the heat, and stir until smooth.
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Spread the frosting atop the brownies. Place them in the refrigerator for an hour or so, to set; then store them at room temperature, covered, for several days.