Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Line the bottoms with parchment paper.
Step 2: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Stir in ½ cup of the chopped toasted pecans.
Step 3: In a large bowl, cream together the softened butter and 2 cups granulated sugar with an electric mixer until light and fluffy.
Step 4: Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined, being careful not to overmix.
Step 6: Divide the batter evenly between the prepared cake pans. Bake for 28-32 minutes, or until a wooden skewer inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
Step 7: To make the caramel frosting, combine 1 cup granulated sugar and ½ cup butter in a heavy-bottomed saucepan over medium heat. Stir until the sugar dissolves and the butter melts.
Step 8: Bring the mixture to a boil and cook for 5-7 minutes without stirring, until it reaches a deep amber color. (If using a candy thermometer, cook to 320°F/160°C).
Step 9: Carefully and slowly whisk in the heavy cream. Be cautious as the mixture will bubble vigorously. Continue to whisk until smooth. Remove from heat and stir in 1 teaspoon vanilla extract and a pinch of salt. Let the caramel cool completely, stirring occasionally, until it reaches a thick, spreadable consistency (about 1-2 hours).
Step 10: Once cooled, you can gradually beat in powdered sugar until the frosting reaches your desired consistency and sweetness. This step is optional depending on how thick your caramel became during cooling.
Step 11: To assemble, place one cooled cake layer on a serving plate. Spread about ⅓ of the caramel frosting over the top. Place the second cake layer on top and spread the remaining frosting over the top and sides of the cake.
Step 12: Garnish the top and sides of the cake with the remaining ½ cup chopped toasted pecans. Slice and serve immediately or store as directed.