Preheat oven to 350ºF. Coat an 8-inch square baking pan with cooking spray; line pan with parchment paper, leaving a 2-inch overhang on all sides. Coat parchment with cooking spray.

Place chocolate, butter, and espresso powder in a large microwavable bowl. Microwave on HIGH until melted, about 1 ½ minutes, stirring after every 30-second interval. Whisk in brown sugar and granulated sugar until well combined, about 30 seconds.

Gradually whisk in eggs and 2 teaspoons of the vanilla until well combined, about 30 seconds.

Sift together flour, cocoa, baking powder, and ½ teaspoon of the salt in a medium bowl until well combined. Gradually fold flour mixture into chocolate mixture just until combined.

Pour half of batter into prepared pan, smoothing into an even layer with a small offset spatula.

Heat caramels, cream, and remaining 2 ¼ teaspoons vanilla and ½ teaspoon salt in a medium saucepan over medium, stirring often, until caramels are melted and smooth, about 5 minutes.

Reserve ⅓ cup caramel mixture in a small, microwaveable bowl. Pour remaining caramel mixture evenly over batter in pan. Top evenly with small dollops of remaining batter, covering as much caramel mixture as possible.

Bake in preheated oven until edges are set and top is dry, puffed, and just slightly cracked, about 30 minutes. Let cool in pan on a wire rack 20 minutes. Using parchment overhang, remove brownies from pan, and cool completely on a wire rack, about 2 hours.

Cut into bars using a large, sharp knife. Microwave reserved caramel on HIGH in 10-second intervals until loosened; drizzle caramel over brownies. Store leftover brownies in an airtight container for 5 to 7 days.