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1
Measure flours, oats, wheat bran, brown sugar, baking power, salt, and cinnamon into the bowl of a food processor and pulse until ingredients are mixed and oats broken down. Add butter and pulse until pieces resembles coarse meal, 8 to 10 one-second pulses.
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2
Stir vanilla into the milk and, with processor motor running, add liquids to the dry ingredients in a thin stream. Continue processing until dough comes together. Divide into two equal portions and flatten into 1/2-inch discs. Wrap each portion in plastic and refrigerate until firm enough to roll out, about two hours.
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3
Meanwhile, make the filling. Place blueberries and water into a small, heavy-bottomed sauce pan and bring to a boil. Reduce heat and simmer gently, covered, for 20 minutes, stirring occasionally. Transfer fruit and water to a food processor and process until broken down into a rough puree. Transfer filling to a bowl, cover, and refrigerate until needed.
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4
When ready to assemble the bars, adjust oven rack to center position and preheat oven to 350u00b0F.
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5
Flour rolling surface and place one portion of the dough in the center. Flour top of dough and roll into an 8- by 12-inch rectangle, turning regularly to prevent sticking. Cut dough in half the long way to create two 4- by 12-inch sheets. To aid with filling and shaping the bars, place each strip of dough on a similarly sized piece of baking parchment before proceeding. Brush any excess flour from dough surface with a dry pastry brush.
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6
Spread an even 1-inch strip of filling (about 2 1/2 tablespoons) down the 12-inch center line of each piece of dough. Using the edge of the parchment as an aid, fold one long side of the dough over the filling, covering it slightly more than half way. Brush a light coating of the egg wash over the remaining edge and, again using the parchment to help keep things even, fold the second dough edge so that it overlaps the first by 1/4 inch. Press gently to seal and flip the bars over so that they are seam-side down. Cut each log into three 4-inch portions.
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7
Brush any excess flour from dough surface with a dry pastry brush. Coat each bar with a thin layer of the egg wash and sprinkle tops with wheat bran. Leave bars on parchment strips and transfer to baking sheet.
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8
Repeat steps five through seven with remaining dough and filling.
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9
Bake bars until just golden, 16 to 18 minutes. Transfer to a wire rack until cool. Store at room temperature in an air-tight container for up to 5 days
