Prepare the red velvet cake according to the package instructions. Pour the batter into a 9×13-inch baking dish, spreading it evenly so it bakes with a uniform thickness.
Bake until the top springs back lightly when touched or a toothpick inserted into the center comes out clean. Once baked, remove the cake from the oven and allow it to cool for 10 minutes so it firms slightly while staying warm enough to absorb the filling.
Poke the Cake
Use the handle of a wooden spoon to poke holes all over the cake. Space the holes evenly so the filling can soak deeply into every slice. Press straight down without twisting to avoid tearing the cake.
Add Sweetened Condensed Milk and White Chocolate
In a small bowl, combine the sweetened condensed milk and melted white chocolate. Stir until smooth and glossy. The mixture should be pourable and cohesive.
Slowly pour the mixture over the warm cake, allowing it to seep into the holes. Tilt the pan gently if needed to help distribute the filling evenly. Let the cake absorb the mixture for at least 30 minutes, then cool completely before frosting.
