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In bowl, beat butter with granulated sugar until light and fluffy; beat in egg.
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In separate bowl, whisk together flour, cocoa, cinnamon, baking soda, baking powder, cloves and salt; add to butter mixture alternately with milk, making two additions of each and scraping down bowl between additions.
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Stir in chocolate chips and chopped walnuts. Cover and refrigerate for 2 hours or until firm.
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Roll by generous 1 tbsp into 1-inch balls. Place, 2 inches (5 cm) apart, on parchment paper-lined baking sheets.
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Bake in top and bottom thirds of 350 F (180 C) oven, rotating and switching pans halfway through, for about 12 minutes or until tops begin to crack. Transfer to rack; let cool completely.
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Glaze: Place rack on baking sheet. In bowl, whisk together sugar, coffee and vanilla; spoon 1 tsp (5 mL) on each cookie. Let set. (Make Ahead: Store layered between waxed paper in airtight container for up to five days.).