Prepare the burnt sugar syrup first so it has time to cool. Make sure you have boiling water at the ready. For the burnt sugar syrup, place sugar in a medium saucepan over medium heat. Stirring constantly with a wooden spoon, cook until the sugar has completely melted and is amber brown, about 8-10 minutes. Turn the heat to low and very carefully and slowly drizzle in the boiling water, a little at a time. Stir after each addition and stand back, as the mixture will rapidly sizzle and bubble. After all of the boiling water is stirred in, stir and cook the sugar syrup for 3 more minutes on low. Turn off the heat and let it cool completely, overnight preferred.

Preheat oven to 350°F (177°C). Grease two 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper.

Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.

Using a handheld or stand mixer fitted with a whisk attachment, beat the butter and sugar together on high speed until creamed, about 2 minutes. With the mixer running on medium speed, pour in ½ cup of the cooled burnt sugar syrup. Beat until combined. Beat in the egg whites, sour cream, and vanilla extract. With the mixer on low speed, add the dry ingredients just until combined. With the mixer still running on low, slowly pour in the milk until combined. Do not over-mix.

Pour batter evenly into prepared cake pans. Bake for 23-25 minutes or until the cakes are baked through. Allow cakes to cool completely in the pans set on a wire rack.

As the cakes cool, prepare the salted caramel. Make sure the salted caramel isn’t too hot anymore before using.

In a large bowl using a handheld mixer or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about 1-2 minutes. Add confectioners’ sugar, remaining ½ cup of cooled burnt sugar syrup, vanilla extract, milk/cream, and salt. Beat on low speed for 30 seconds, then increase to high speed and beat until completely combined, about 2 minutes.

Assemble and frost: Slice a thin layer off the tops of the cakes to create a flat surface. Place 1 cake layer on your cake stand. Using a large icing spatula, evenly cover the top with frosting. Drizzle ¼ cup of salted caramel on top of the frosting. Top with 2nd cake layer. Refrigerate the cake for at least 30-45 minutes before finishing the frosting and garnish. Spread the remaining frosting all over the top and sides. Garnish with toasted pecans and more salted caramel. Slice and serve.

Cover leftover cake tightly and store in the refrigerator for up to 5 days.