Preheat oven to 350° F. Move oven rack to lowest position. Spray a 10-inch bundt pan with nonstick cooking spray. Place a roasting pan half filled with water in the oven.
Heat sugar in smallheavy-duty saucepan over medium-low heatstirring constantlyfor 3 to 4 minutes or until dissolved and caramel colored. Quickly pour onto bottom of prepared Bundt pan; swirl around bottom to coat.
Mix egg yolkssweetened condensed milk and evaporated milk in large bowl until well blended.
Prepare cake mix batter according to package directionsusing wateroil and eggs.
Pour egg and milk mixture over caramel. Slowly add cake batter over the flan. Place pan in roasting pan in the oven.
Bake for 50 to 60 minutes or until wooden pick inserted in middle comes out clean. Remove pan from water. Let cool before inverting cake onto a serving dish.