In a medium-sized bowl, sift together the flour, baking powder, baking soda and salt. Set aside. In the bowl of a stand mixer (or using a hand mixer), cream together the butter, sugar and light brown sugar until it is light and fluffy. Add the eggs one a time. Add the vanilla extract. In a separate small bowl, mix together the sour cream and ½ cup of burnt sugar syrup. You will have extra syrup. Save it--it’s delicious in coffee!
Add ⅓ of the flour mixture to the butter, sugar and eggs, mixing just until the flour is incorporated, then add ⅓ of the sour cream/burnt sugar syrup mixture. Repeat until you have a uniform cake batter, taking care not to overmix. Scoop the batter into a well-greased 10-12 cup Bundt pan.
Bake at 350 degrees F until the top springs back when you press it and a cake tester comes out clean, about 1 hour.
Let cool completely before unmolding and icing.