In a medium bowl. mix together the butter, sugar and graham cracker crumbs.
Lightly grease and line a 9-inch x 13-inch baking pan with parchment paper.
Press the crumb mixture evenly into the prepared pan.
Combine boiling water and Jell-o; stir until dissolved.
Add sweetened milk, lemon juice and strawberries, including the syrup.
Fold in marshmallows and whipped cream.
Spread over prepared base and chill until the Jell-o has set.
These can also be served frozen; in fact many people prefer them frozen and that's almost always how I serve them.
They defrost pretty quickly, so I always store these in the freezer anyway.