To make the caramel sauce, heat the cream in a small saucepan over medium-low heat, just until small bubbles form around the edges.

Meanwhile, combine the water, 2 cups of sugar, and corn syrup in a medium saucepan over high heat, stirring until the sugar dissolves. Bring to a boil and cook for 6 to 8 minutes, until a candy thermometer registers 350°F and the mixture is a deep amber color. Remove from the heat and let cool for 1 minute. Add the cream and stir until combined. Whisk in the sour cream. Set aside and let cool to room temperature.

To make the brownies, preheat the oven to 375°F. Line a 9-inch square baking dish with parchment paper.

Melt the butter and chocolate in the top of a double boiler placed over simmering water, stirring until smooth and completely melted.

Meanwhile, whisk together the eggs, remaining 1 1/2 cups of sugar, and vanilla in a large bowl. Whisk together the flour and salt in another bowl. Add the melted chocolate to the egg mixture and whisk to combine. Gently fold in the flour.