Step 1

In a small bowl, mix milk with the warm water. Add the yeast and whisk gently until it dissolves. Let sit for 5 minutes, until the mixture begins to foam.

Step 2

Cream together the butter, sugar and salt on medium speed, until light and fluffy, about 3 minutes. Scrape down the sides of bowl and beat in the egg. Reduce the speed to low and add the flour in three additions, alternating with the milk mixture, scraping down sides of bowl between each addition. Increase the speed to medium and beat the dough until it forms a smooth mass and pulls away from sides of bowl, 7 to 10 minutes.

Step 3

Press the dough into an ungreased 9x13-inch baking dish. Cover with plastic wrap, place in a warm spot and let rise until doubled, about 2½ to 3 hours.

Step 4

Preheat oven to 350 degrees F. To prepare the topping, whisk together the corn syrup, water and vanilla extract in a small bowl. Cream together the butter, sugar and salt on medium speed until light and fluffy, about 5 to 7 minutes. Scrape down sides of bowl and beat in the egg. Reduce the speed to low and add the flour in three additions, alternating with the corn syrup mixture, scraping down sides of bowl between each addition.

Step 5

Drop the topping by large spoonfuls over the risen dough and use an offset spatula to gently spread it into an even layer. Bake for 40 to 45 minutes; cake will rise and fall in waves and have a golden brown top, but will still be liquid in center when done. Place the pan on a wire rack and cool completely to room temperature before serving. Dust with powdered sugar, if desired. This cake is best eaten the same day it's made, but leftovers can be stored in an airtight container at room temperature for up to 1 day.