In food processor, grind the graham cracker squares into fine crumbs. Place crumbs into a medium bowl and add melted butter. Stir with fork.
2In food processor, grind mini chocolate chips and add to graham cracker mixture. Press graham cracker mixture onto bottom and up sides of 2 tart pans (4 1/2" pans). Bake for 7 minutes. Place tarts in freezer for 10 minutes to cool.
3In large bowl, mix your heavy cream with sugar until light and fluffy, freeze until ready to use.
4In medium bowl, add peanut butter, sweetened condensed milk, and lemon juice and mix with beater until all ingredients are well blended. Add the remainder 1/4 cups of mini chocolate chips. Fold into whipped cream.
5Fill tart pans with peanut butter mixture. Garnish with mini chocolate chips. Keep chilled until ready to serve.