Yields 16 servings.
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Whisk well in large bowl and set aside:
Add the flour mixture in thirds to the chocolate mixture, whisking each addition in gently.
Line 8" square pan with parchment paper.
Pour mixture into pan.
Bake 30-35 minutes. (Note that it may take longer in a non-aluminum pan.)
Cool completely (1 hours). It will flatten out as it cools.
Tightly seal leftovers in foil to keep moist.