To make caramel layer, melt butter and sugar in a medium saucepan. Add corn syrup and condensed milk and stir until it comes to a boil. Turn down to simmer and simmer 7-10 minutes until mixture achieves deep golden color, stirring constantly. (For most consistent results, use a candy thermometer and simmer until caramel reaches 235*-240*). Remove from heat, stir in vanilla and pour onto brownies in pan, distributing caramel evenly with a spatula. Do not scrape sides and bottom of the pan so that you do not get any burned sugar crystals. Place in fridge to cool while you make chocolate ganache layer. Sprinkle with salt if desired.