1. Heat oven to 350°F. Spray bottom and sides of 13x9-inch pan with cooking spray.
2. In large bowl, beat cake mix, water, oil, eggs, cinnamon and nutmeg with electric mixer on medium speed 2 minutes, scraping bowl occasionally. Stir in carrots. Pour into pan.
3. Bake 26 to 33 minutes or until toothpick inserted in center comes out clean. Remove cake from oven to cooling rack. Immediately poke holes using fork over top of cake, wiping fork tines occasionally with paper towel to reduce sticking.
4. While cake is still warm, evenly pour and gently spread 3/4 cup caramel sauce over cake, working back and forth to fill holes. Rap pan on counter several times to help caramel sauce flow down holes. Refrigerate 2 hours.
5. When ready to serve, in large bowl, beat cream cheese and softened butter with electric mixer on medium-high speed until smooth. On low speed, beat in vanilla and powdered sugar until frosting is smooth and creamy. Drop frosting by spoonfuls; spread evenly on top of cake. Drizzle 2 tablespoons caramel sauce over top.
6. Cut into 4 rows by 3 rows. Sprinkle with sea salt, if desired. Cover and store remaining cake in refrigerator.