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Preheat oven to 350°F Line a 15x10x1-inch baking pan with foil.
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In a medium bowl, using an electric mixer set on high speed, beat butter and brown sugar until light and creamy.
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On medium speed, beat in egg.
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In another bowl, combine flour, baking soda and 1/2 teaspoon cinnamon.
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Gradually add flour mixture to butter mixture and mix until dough is smooth. Stir in oats and walnuts.
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Reserve 1 cup dough for topping. Press remaining dough into bottom of prepared pan.
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In a medium saucepan, heat 1 1/2 cups chocolate chips, condensed milk, instant coffee and remaining cinnamon over medium heat; stir until smooth.
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Spread mixture evenly over the dough in the pan, smoothing the surface with a spatula; crumble reserved dough on the top.
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Sprinkle with the remaining chocolate chips. Bake until lightly browned, about 20 minutes. Cool completely on a wire rack. Lift foil to remove from pan; cut into 2-inch bars.