Dissolve 1/4 teaspoon baking soda in boiling water; stir in syrup and vanilla. Set aside. Combine flour, sugar, 1/4 teaspoon baking soda and the salt in medium mixing bowl; cut in butter until mixture resembles coarse crumbs. Set aside 1 cup each of chocolate mixture and crumbs; gently combine remaining chocolate and crumbs, stirring just until crumbs are moistened. (Mixture will be lumpy.) Pour reserved 1 cup chocolate mixture into unbaked pastry shell; evenly pour in chocolate crumbs mixture. Sprinkle with remaining 1 cup crumbs; dust with cinnamon. Bake at 375 degrees for 1 hour. Cool completely.
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