Line two large baking sheets with nonstick baking mats, such as Silpats, or with parchment paper. Dip a 2-inch round cookie cutter in flour, and mark circles 1 inch apart on the prepared sheets. Transfer Pâte à Choux to a pastry bag fitted with a 5/8-inch plain tip (such as an Ateco #808), and pipe puffs to fit in the floured circles. Gently smooth the pointed peaks with a moistened finger, rounding tops to ensure even rising. Freeze puffs (on sheets) until firm, about 30 minutes.
Meanwhile, in a saucepan, combine cream, milk, and corn syrup; bring to a simmer over medium-high heat. Remove from heat; add chocolate, stirring with a wooden spoon until melted. Set chocolate sauce aside to cool slightly. Preheat the oven to 375°F.
Remove puffs from freezer. Bake, rotating sheets halfway through, until puffs are golden brown, 25 to 30 minutes. Transfer sheets to wire racks to cool completely. Using a serrated knife, slice off the top third of each puff; set aside. Place a scoop of ice cream on the bottom of each puff; replace tops. Drizzle with sauce. Serve immediately.
