Preheat oven to 350 degrees. Line a 9x13 baking dish with parchment paper, or spray with cooking spray (I like the one with flour in it.)
In the bowl of a stand mixer (or large bowl if using a hand mixer), cream together the butter and sugar until smooth.
Add flour and salt and mix until crumbly.
Press 1 3/4 cups crumb mixture into the bottom of the prepared baking dish.
Bake for 10-12 minutes or until golden brown. Remove, but leave oven on.
In a medium, microwave-safe bowl, combine the sweetened condensed milk and bittersweet chips and heat on medium heat, in 30 second intervals in microwave until chips are melted. Stir until smooth.
Pour over hot crust and spread until even.
Sprinkle reserved crumb mixture over chocolate mixture and then drop small teaspoonfuls of the raspberry preserves all over the top.
Sprinkle with the semi-sweet chocolate chips and return to oven and bake for 25-30 minutes, or until set.
Allow to cool, and then cut into bars.