In the bowl of an electric mixer, beat the butter until smooth. Add the sugar, vanilla, and salt and mix well. Add the flour in 2 portions, mixing well with each addition. Stir in the butterscotch chips, 1/2 cup of the chocolate chips, and the nuts. The mixture will be crumbly.
Pour the batter into a 9 1/2" x 14" jelly roll pan. Press into an even layer. Bake for 20 minutes or until golden brown. Cool.
While the brittle is cooling, warm the remaining 1/2 cup chocolate chips in the microwave for 30 seconds. Stir. Continue heating the chocolate in the microwave in 10-15 second bursts until it is thin and smooth. Transfer to a decorating bag or resealable bag, cut the tip and drizzle of the slightly warm brittle.
When the cookie brittle is completely cool break or cut the brittle into pieces. Enjoy.