Anthocyanins are responsible for the red, blue and purple pigments found in fruits and vegetables. They are part of the flavonoid family and certain foods, such as blueberries, are packed with them. Anthocyanins are recognized for their antioxidant powers, fighting the cellular damage brought on by free radicals in the body, and some studies suggest that they may help improve memory.
Combine the butter and graham crackers in the bowl of a food processor and pulse until finely ground and the mixture holds together when pinched. Transfer to a 9-inch tart pan with a removable bottom, and press evenly along the bottom and about halfway up the sides. Place on a baking sheet and bake until lightly golden, about 10 minutes. Let cool completely.
Combine 1/3 cup of the sugar, the sour cream and cream cheese in a stand mixer fitted with a paddle attachment (or a large bowl if using a hand mixer), beat until smooth. Add the lemon zest, vanilla and eggs, and continue to beat until incorporated. Pour into the cooled tart shell and bake on a baking sheet until set, 25 to 30 minutes. Cool to room temperature and refrigerate until chilled, at least 1 hour up to overnight.
About 30 minutes before serving, toss the berries with the remaining 2 tablespoons of sugar, mash slightly with a wooden spoon and let sit at room temperature. Spoon the berries and collected juice over the tart. Serve.