HEAT oven to 350°F.
BEAT first 6 ingredients in large bowl with mixer until blended. Stir in chopped nuts and chocolate. Pour into greased and floured 13x9-inch pan. Top with 24 caramels, spacing evenly in batter.
BAKE 45 to 50 min. or until toothpick inserted in center comes out clean. Cool 10 min. Remove cake to wire rack; cool completely.
MICROWAVE remaining caramels and 1 Tbsp. water in microwaveable bowl on HIGH 1 to 1-1/2 min. or until caramels begin to melt. Stir until caramels are completely melted and mixture is well blended. Carefully spread onto cake. Top with pecan halves.