Swirled Caramel Sheet Cake with Fudgy Chocolate Frosting

1. Preheat the oven to 350° F. Line a 9×13 inch baking dish with parchment paper.2. In a large bowl, beat together the butter and sugar until fluffy. Add the vanilla, beating until smooth. Beat in the eggs, one at a time, until combined. Add the flour, baking powder, baking soda, and salt. Stream in the milk, beating until just combined. 3. To make the caramel. Melt together the butter, brown sugar, and maple in a medium saucepan. Bring to a boil and cook 4-5 minutes, until thickened slightly. Stir in the vanilla and salt. 4. Pour 2/3 of the batter into the prepared pan. Drizzle half the caramel over the batter, then pour over the remaining batter (it will not cover the caramel fully). Then drizzle over the remaining caramel. Use a knife to lightly swirl the caramel around, don't over mix. Bake for 30 to 35 minutes, until the center is just set. Let cool completely. 5. To make the chocolate frosting. Microwave the chocolate chips and a pinch of salt, stirring every 30 seconds, until melted. Stir in the sour cream and espresso, a dollop at a time, until the mixture is smooth. Swirl the frosting onto the top of the cake. If desired top with chocolate. Slice, eat, and enjoy!!