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1
Preheat an oven to 350 degrees F (175 degrees C).
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2
Lightly grease a baking sheet, or line with parchment paper.
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3
Combine the flour, salt, cocoa powder, baking powder, cinnamon, and coffee granules in a bowl.
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4
Set aside.
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5
Beat the butter and sugar with an electric mixer in a large bowl until smooth.
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6
Add the eggs one at a time, allowing each egg to blend into the butter mixture before adding the next.
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7
Beat in the vanilla with the last egg.
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8
Mix in the flour mixture until just incorporated.
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9
Fold in the chocolate chips and walnuts; mixing just enough to evenly combine.
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10
Dived the dough in half and shape each into 8x2 inch flat rectangles about 1 inch thick.
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11
Place on the baking sheet 3 to 4 inches apart.
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12
Beat egg yolk with water in a small bowl.
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13
Brush over the top of each loaf.
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14
Bake in the preheated oven until both loaves are firm, 20 to 25 minutes.
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15
Remove from the oven and cool for 10 to 12 minutes.
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16
Reduce oven heat to 300 degrees F (150 degrees C).
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17
Cut each loaf diagonally into 3/4 inch slices.
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18
Place each slice, cut-side up onto the baking sheet.
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19
Return to the oven and bake until the biscotti are dry, 10 to 15 minutes on each side.
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20
Cool in the pans for 10 minutes before removing to cool completely on a wire rack.
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21
Store in an airtight container.
