Preheat your oven to 350 degrees. Line either an 8 or 9 inch pan with parchment paper and set aside.
Whisk together your flour, cocoa and salt. Set aside.
In a heat proof bowl combine the chocolate chips with the butterscotch. Melt in the microwave for 2 minutes or until melted, stirring every 20 seconds to prevent burning. Set aside.
Cream together the butter and sugar in the bowl of an electric mixer until fluffy. Add the eggs and vanilla. Stir until completely incorporated. Drizzle in the melted chocolate. Mix until combined.
Fold the dry ingredients followed by the Guinness and chocolate chips if using. Pour into your prepared pan and bake 35-40 minutes or until a toothpick comes out clean.