Melt two cups of the white chocolate chips according to directions and spread out over a foil lined 10 by 15 inch pan. (Be careful not to spread too thin, you won't end up going to the edges of the pan.)
While waiting for the chocolate to dry, cream together the butter, sugar, salt, and vanilla until fluffy.
Add in 2 cups of all purpose flour until fully combined, the mixture will be very crumbly.
Pour in the sweetened condensed milk and fully combine, scraping down the sides and bottom of the bowl as necessary.
If the mixture is too sticky and not dough like, add a tablespoon of flour at a time until you get the desired consistency.
Spread the cookie dough over the hardened white chocolate. Put in the freezer for 15 minutes.
While it is in the freezer, melt the rest (2 cups) of the white chocolate chips. Get your Trix ready to put on top of the chocolate.
Pull the pan out of the freezer and working quickly spread the melted chocolate over the cookie dough layer and then quickly pour on the Trix and press down, adding more cereal if needed.
If the chocolate hardens before you are able to get all of the Trix in place, pop the whole pan (Trix and all) into a 400 degree oven for about 5 minutes or until you are able to press the cereal into the chocolate.