Caramel guinness brownies

In a medium saucepan, combine sugar, cream of tartar, and 1/2 cup of water. Cook over high heat without stirring until sugar begins to melt and edges turn golden. Swirl the pan to cover evenly, and continue cooking until the sugar turns golden amber. Wear oven mitts (sugar will be extremely hot and may splatter) while carefully pouring the heavy cream down the side of the pan, stirring constantly with a whisk or wooden spoon until combined. Transfer to a medium bowl to cool.
(Note: This caramel with be very thick and chewy. For a thinner caramel, use more cream.)
Preheat the oven to 350 degrees and grease a 9x13 inch baking pan.
In a large bowl, whisk together flour and cocoa. In a double boiler melt butter, unsweetened chocolate, white chocolate, and semi sweet chocolate; whisk together until smooth. In a medium mixing bowl, beat eggs and sugar until fluffy. Whisk melted chocolate and Guinness into four/cocoa mixture. Then, mix in egg/sugar mixture. Stir in milk chocolate chips. Spoon half the batter into the prepare pan, being sure to get about half the chocolate chips. Dollop about 5 tablespoons of caramel on different spots on the batter in the pan, streaking the caramel so that there will be just a touch of caramel per brownie. You will only use about half of the prepared caramel (the rest would be nice with apples!). Pour the remaining brownie batter in the pan and bake for 25 to 30 minutes.
Beat all icing ingredients together in a small bowl and spread over warm brownies.