Preheat oven to 375 degrees F. Line a 9x13" rectangular metal baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray; set aside.
In a medium saucepan, combine the butter and 14 caramels (about 1/2 cup). Heat over medium-low, stirring constantly until caramels soften and melt. Remove from heat and let set for about 3-5 minutes.
Whisk in the brown sugar, followed by the eggs, one at a time, whisking very well after each addition so as not to scramble the eggs, followed by the vanilla extract. Add in the flour, baking soda and salt and mix well until a soft batter comes together.
Pour about half of the batter into the bottom of the prepared pan evenly. Bake for 10-12 minutes, until just about set. Remove from oven but keep oven on.
While bars partially bake, make the filling. Combine remaining 1 & 1/2 cups caramels (about 34 caramels total) with heavy cream and microwave in a microwave-safe bowl for 30 seconds - 1 minute, stirring until melted and smooth.
Once base layer is partially baked, pour the caramel mixture on top evenly, followed by the remaining blondie batter. Sprinkle the tops with flaky sea salt. Return to the oven and bake for an additional 20-25 minutes or until set and center is golden brown. Cool completely before cutting into bars.