Heat oven to 350°F (325°F for dark or nonstick pan). Grease 13x9-inch pan, or spray with baking spray with flour.
In large bowl, mix cake mix, butter and 1/2 cup of the evaporated milk with spoon until well blended. Using a piece of plastic food wrap, press half of dough (about 1 1/4 cups), in pan; remove wrap. Bake 12 minutes.
Meanwhile, in 1-quart saucepan, heat caramels with remaining 1/3 cup evaporated milk over low heat, stirring occasionally, until melted.
Remove partially baked crust from oven. Sprinkle 1/2 cup of the candies evenly over crust. Drizzle with caramel mixture to within 1/2 inch of the pan sides. Drop remaining batter by rounded teaspoonfuls over caramel mixture. Sprinkle with remaining 1/2 cup candies; press in lightly with spoon.
Bake 20 to 24 minutes longer or until center is set and looks dry and puffy. Cool 10 minutes. Run knife around sides of pan to loosen edges of bars. Cool completely, about 1 1/2 hours. Cut into 8 rows by 4 rows. Store covered.