Preheat the oven to 350°F and prepare a loaf pan.
Using an electric mixer on low speed, mix the sour cream, brown sugar, eggs, and vanilla extract until well blended.
Stop the mixer and add the flour, baking powder, baking soda, and salt. Mix on low until well combined.
Fold in the chopped apples and half of the chopped walnuts. The batter will be very thick.
Transfer the batter to the prepared loaf pan.
Sprinkle the remaining walnuts over the top and gently press them into the batter without pushing them too deeply.
Bake at 350°F. The recipe card lists 50 minutes, while the instructions specify 60 minutes. Begin checking around 50 minutes and continue baking as needed until the bread is done.
Remove the bread from the oven and let it cool in the pan for 20–30 minutes before carefully removing it.
To make the praline sauce, combine the butter and brown sugar in a saucepan.
Bring the mixture to a boil over medium heat, then simmer until it thickens into a sauce.
Let the bread cool, drizzle the praline sauce over the top, and serve.