How to Make It
Combine milk and 2 tablespoons warm water in a bowl, stirring with a whisk. Dissolve yeast in milk mixture. Let stand 5 minutes. Place canola oil and next 3 ingredients (through salt) in a large bowl; beat with a mixer at medium speed until well blended (about 1 minute). Add egg, beating well. Weigh or lightly spoon 9 ounces (about 1 3/4 cups) flour into dry measuring cups; level with a knife. Add flour and milk mixture alternately to sugar mixture, beginning and ending with flour. Beat 5 minutes or until dough is smooth and pulls away from sides of bowl.
Pat dough into bottom of a 13 x 9-inch metal baking pan coated with baking spray; cover with a damp towel. Let rise in a warm place (85°), free from drafts, 2 hours or until doubled in size.
Preheat oven to 350°. Combine corn syrup, 2 tablespoons water, and vanilla in a bowl, stirring with a whisk. Place 1 1/2 cups granulated sugar, 9 tablespoons butter, and 1/2 teaspoon salt in a large bowl; beat with a mixer at medium speed until fluffy (about 3 minutes). Add egg, beating well. Weigh or lightly spoon 2 ounces (about 1 cup plus 3 tablespoons) flour into a dry measuring cup; level with a knife. Add flour and corn syrup mixture alternately to sugar mixture, beginning and ending with flour mixture. Dollop topping over dough, and spread to edges of pan.
Bake at 350° for 35 minutes or until top is golden brown. Cool completely in pan on a wire rack. Sprinkle with powdered sugar, and cut into squares.
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