4 (1 ounce) squares unsweetened chocolate, chopped
3 eggs, beaten
1 1/4 cup vegetable oil
1 cup white sugar
1 (14 ounce) can sliced carrots, drained
2 cups all-purpose flour
1/2 teaspoon baking powder
Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan. Cut each one of the four cake layers into 16 squares. Place 1 cup of the chopped chocolate in the bottom of each square. Sprinkle cake with remaining chopped chocolate. Fold edges of squares into center of the cake, leaving 1-inch border. Secure with toothpicks.
Pour the oil into the bottom of a large skillet over medium high heat. Place the carrots and sugar in the center of the oil. Cook, stirring, until sugar is dissolved, about 7 minutes. Remove from heat. Using a wooden spoon or knife, remove the buttercream from the bowl and place in the center of the caramel layer. When sugar has melted, turn over and spread caramel layer onto bottom of 9x13 inch pan. Brush the buttercream with water to keep warm while baking. Cool completely.
To make the frosting, press 1 cup of the chocolate filling into the center of the stick wrap. Spread evenly on top of the carrot cake, then spread evenly on top of the carrot cake. Warm the remaining buttercream with a wire whisk; sprinkle on top of carrot cake, spreading evenly with remaining chocolate filling. Frost top of frosting with remaining chocolate filling. Chill cake overnight.