Bake cake according to package directions, once baked remove from oven and poke holes over top of cake with handle of wooden spoon, set aside.
To make your raspberry sauce in a medium saucepan add water, raspberries, lemon juice and sugar.
Heat for about 5 minutes over medium high heat until the raspberries break down while you mash them around with a spoon.
Remove from heat and strain out seeds (if desired) through a fine mesh strainer.
Return sauce to pan and place back on heat.
In a small bowl whisk together your 2 Tbs water and cornstarch and stir into sauce for about 1 minute until slightly thickened.
Remove from heat and stir in your vanilla and salt.
Pour your can of sweetened condensed milk over top of cake and using spatula spread over top of cake and into holes.
Then spread over your raspberry sauce over top of cake and again spread over top of cake and into holes.
Place in refrigerator for 1-2 hour until raspberry sauce is set up slightly.
Remove from refrigerator and top with whipped topping.
Garnish with lemon slices and raspberries if desired.