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1
Blend sugar,cocoa powder, and cinnamon in small bowl.
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2
Whisk sugar, flour, and espresso powder in heavy medium saucepan to blend. Gradually add milk, whisking until smooth. Whisk in yolks and salt. Add butter. Cook over medium-high heat until pastry cream thickens and boils, whisking constantly, about 6 minutes. Whisk in vanilla. Transfer to small bowl. Press plastic wrap directly onto surface of filling. Chill until cold, at least 4 hours and up to 2 days.
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3
Combine yeast and 1/4 teaspoon sugar in large bowl of heavy-duty mixer. Pour warm milk over and stir to blend. Let stand until yeast dissolves and mixture bubbles, about 10 minutes.
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4
Meanwhile, whisk flour, cinnamon, salt, and 1/4 cup sugar in medium bowl to blend. Whisk butter and eggs in another medium bowl to blend.
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5
Butter large bowl. Using dough-hook attachment, beat butter-egg mixture into yeast mixture on medium-low speed until well blended, stopping occasionally to scrape down sides of bowl, about 4 minutes. Beat in flour mixture by 1/4 cupfuls, then beat dough until smooth and beginning to pull away from sides of bowl, about 5 minutes. Scrape dough from hook into bowl. Let dough rest 5 minutes. Scrape dough into buttered bowl (dough will be sticky). Turn dough to coat with butter. Cover bowl with plastic wrap and refrigerate dough overnight. Sprinkle 2 baking sheets lightly with flour. Gently press dough to deflate. Roll out chilled dough on lightly floured surface to 1/3-inch thickness. Using 2 3/4- to 3-inch-diameter round cutter, cut out dough rounds. Transfer rounds to floured sheets, spacing 2 inches apart. Gather dough scraps. Roll out to 1/3-inch thickness; cut out more rounds. Repeat until all dough is used. Cover dough rounds on sheets with towels. Let rise in draft-free area until doubled in volume, about 1 hour.
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6
Line 2 baking sheets with several layers of paper towels. Pour oil into large deep skillet to depth of 1 1/2 inches. Attach deep-fry thermometer and heat oil to 360u00b0F to 370u00b0F. Fry 3 dough rounds at a time until golden brown, adjusting heat to maintain temperature, about 1 1/2 minutes per side. Using slotted spoon, transfer doughnuts to paper towels to drain. Dip both sides of warm doughnuts into topping. Transfer to rack and cool completely.
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7
Spoon filling into pastry bag fitted with 1/4-inch plain round tip. Push blade of small sharp knife into side of 1 doughnut about 3/4 of the way to opposite side; remove knife. Insert tip of pastry bag into slit and press in filling until center of doughnut bulges. Return doughnut to rack. Repeat with remaining doughnuts. (Doughnuts can be filled up to 2 hours before serving.Let stand at room temperature.)
