In a medium bowl, combine the graham cracker crumbs, melted butter, and sugar. Mix well until the crumbs are evenly moistened. Divide the mixture evenly among 6-8 small jars or glasses. Press the crumbs firmly into the bottom of each jar to create a compact crust.

In a large bowl, beat the softened cream cheese with an electric mixer until smooth and creamy. Gradually add the sweetened condensed milk, mixing until well combined. Stir in the lemon juice and vanilla extract until the filling is smooth and lump-free.

Spoon the cheesecake filling evenly over the graham cracker crusts in each jar. Gently smooth the tops. Cover the jars with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the filling to set completely.

In a medium saucepan, combine the raspberries, sugar, lemon juice, and cornstarch. Cook over medium heat, stirring occasionally, until the raspberries break down and the sauce thickens slightly. This should take about 5-7 minutes. Remove from heat and let the raspberry topping cool completely.

Once the raspberry topping has cooled, spoon it evenly over the chilled cheesecake filling in each jar. Garnish with a few fresh raspberries, if desired. Serve immediately or store in the refrigerator until ready to serve.