In a 3- to 4-quart pan over medium-high heat, melt butter, stirring occasionally, about 4 minutes. Remove from heat.
Stir in sugar, then eggs and vanilla, until blended. Stir in salt and baking powder. Add flour and cocoa and stir until batter is smooth.
Butter a 12- by 20-inch piece of foil. Line a 9- by 13-inch pan with foil, buttered side up, letting foil hang over pan ends. Scrape batter into pan. Evenly space caramels over batter.
Bake brownies in a 325° oven just until a toothpick inserted in the center (not in a caramel) comes out clean, 55 to 60 minutes. Let cool.
Lift brownies with foil from pan to a counter. Peel back sides of foil. With a long, hot knife, cut between caramels into 35 squares; occasionally rinse knife in very hot water and wipe clean.