Put hulled berries in a blender and puree until smooth. Pour through a fine mesh strainer into a large bowl, pressing pulp with a flexible spatula to extract as much juice as possible. Discard the solids. Whisk in the sour cream, sugar, lemon juice and vanilla. Stir in the 1/4 cup graham cracker crumbs. Spoon mixture into ice pop molds. Slide in strawberry slices if using and insert sticks. Sprinkle crumbs around base of each pop for garnish if desired. Freeze until firm, at least 6 hours or up to 1 week. To unmold pops, run hot water over outsides of the molds for a few seconds, then gently pull the sticks. Makes 6 pops.