Combine the graham cracker crumbs, the sugar, and melted butter together until fully combined. Press the crust firmly and evenly into the bottom of a 9x9 square baking pan. I like to spray it lightly and then line with a long piece of parchment so I can lift out the chilled bars for neater cutting. This is optional. Chill the crust while you make the filling.

Put the chopped rhubarb and sugar in a saucepan along with 6 tablespoons of water. Bring it up to a boil and simmer until thick and soft...about 5 minutes. Stir frequently so the fruit doesn't scorch. Puree the mixture until completely smooth. Blend in the vanilla and lemon and set aside to cool.

When the rhubarb is cooled blend in the condensed milk.

Whip the cream to stiff peaks. Fold in the rhubarb mixture gently but completely. Spread evenly over the crust and put back in the refrigerator to chill for at least 2-3 hours.

The bars can be served chilled, or even frozen.