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1
Butter a 24-centimeter (about 9-inch) springform pan and line with a round of parchment paper.
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2
Butter paper and remove side of pan.
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3
Stir together sugars and cinnamon.
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4
Roll out dough on a lightly floured surface, dusting with flour as necessary, into a 24- by 9-inch rectangle.
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5
Brush off excess flour with pastry brush and trim edges with a pizza wheel or sharp knife.
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6
Arrange dough so that a long side is nearest you and sprinkle cinnamon sugar over dough, leaving a 1-inch border along bottom edge.
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7
Brush border with some beaten egg and chill remaining egg.
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8
Fold top edge of dough over about 1 inch.
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9
Using both hands, roll dough toward you: Use your thumbs to tuck dough under and tighten as you go, working your way down entire length of log (as when rolling up a poster), and gently rock dough back and forth to keep it taut and even.
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10
When finished, roll log back and forth over seam to seal.
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11
Transfer log, seam side down, to bottom of springform pan, bringing both ends of log together to make a ring.
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12
Beginning 2 inches from where ends meet, make vertical cuts from outside of ring toward center at 2-inch intervals, cutting halfway through ring.
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13
Attach side of pan and slide pan into garbage bag, propping up top of bag with inverted glasses to keep it from touching dough, then tuck open end under pan.
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14
Let ring rise until slightly puffy and spongy to the touch, about 2 1/2 hours.
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15
Blend flour and sugar in a food processor.
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16
Add frozen butter and pulse until very finely chopped.
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17
Chill streusel until ready to use.
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18
Preheat oven to 375F.
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19
Gently brush top and center of ring with some of remaining beaten egg, then sprinkle with streusel.
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20
Bake in middle of oven until top is browned and streusel is crisp, about 45 minutes.
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21
Cool in pan on a rack 10 minutes, then run a thin knife around edge to loosen and remove side of pan.
