Preheat oven to 350 degrees F (175 degrees C). Grease a 9-inch round cake pan and set aside.
In a medium bowl, cream together 1/2 cup butter and the brown and white sugars until light and fluffy.
Beat in the eggs, one at a time, then stir in the vanilla.
Combine the flour, baking powder, and salt; stir into the creamed mixture until just blended.
Spread the batter into the prepared pan and bake for 25 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Meanwhile, in a medium saucepan, combine the white sugar, 1/4 cup butter, and cornstarch. Stir in the walnuts and pecans. Cook over medium heat, stirring constantly, until mixture is thick and bubbly. Remove from heat.
Pour the topping over the hot cake and spread evenly. Return to the oven for an additional 30 minutes.
Let cool before serving.
Interesting Facts
The Guadalupe River Bottom Puddin Cake is a traditional Southern dessert.
The cake is a combination of a rich and creamy puddin cake topped with a sweet, crunchy layer of crushed pecans.
The cake is named after the Guadalupe River, which runs through the Texas Hill Country.