Bollen with coffee glaze are based on bassche bollen (chocolate-glazed cream puffs), a specialty of 's-Hertogenbosh, a city in the Netherlands.
Preheat oven to 375 degrees. Heat water and butter in a saucepan over high heat until butter is melted and water is boiling. Remove from heat, and stir in flour and salt. Reduce heat to medium, return pan to heat, and cook, stirring, 1 minute. Stir in eggs a little at a time until smooth. Divide dough into 8 mounds, and place on a parchment-lined baking sheet. Bake until puffed and golden, about 35 minutes. Let cool completely on a wire rack.
Whisk together cream and granulated sugar until stiff, glossy peaks form. Transfer to a pastry bag fitted with a 1/4-inch plain round tip. Push pastry tip through bottom of each puff, and fill.
Whisk together confectioners' sugar, milk, and coffee extract until smooth. Dip tops of puffs in glaze, and let set on a wire rack 30 minutes. Serve immediately.