Preheat oven to 350 degrees. Line a standard size 12-count muffin pan with paper liners. Set aside. Recipe makes 20 mini pies. If you have an additional muffin pan line 8 more.
In a medium bowl, combine gingersnap crumbs, sugar and melted butter and mix until well combined. Press one heaping tablespoon of crumbs into each liner, packing tightly. If you have any remaining crumbs, just add a bit more into each liner. Bake for 5 minutes. Remove from oven and set aside.
Place 3 containers of the blackberries into a blender and puree until smooth. In batches, press the blackberry puree through a strainer to remove the seeds. I use a rubber spatula to press down on the mixture. When finished with all the blackberry puree, I yielded close to about 1 3/4 cups of seedless puree. To the puree, add the lime juice and the vanilla.
In a medium bowl with a hand mixer, beat the egg yolks until pale yellow. Slowly add the sweetened condensed milk, until well combined and thickened.
Add the blackberry mixture to the egg mixture and beat until well combined. The mixture will be about 4 cups total. Pour the filling evenly into each muffin cup.
Bake for 15 minutes. Pies should be just a bit jiggly in the center. Let cool on a wire rack, then refrigerate for 2-3 hours until firm. Serve with the remaining blackberries on top for garnish with some fresh whipped cream on the side, if desired.