Grease an 8 x 8‑inch baking pan and set aside.

In a large mixer bowl, stir together 1 cup white whole wheat flour, 1 packet Fleischmann's® RapidRise™ yeast, 2 tablespoons sugar, and 1/2 teaspoon salt until evenly combined.

In a microwave‑safe bowl, combine 3/4 cup water and 3 tablespoons Mazola® Corn Oil. Microwave on HIGH in 15‑second increments until the mixture is very warm but not hot to the touch (about 120°–130°F).

Add the warm water–oil mixture, 1 egg, and 1 teaspoon Spice Islands® Pure Vanilla Extract to the dry ingredients.

Beat the mixture 2 minutes at medium speed with an electric mixer, scraping the bowl occasionally.

Add the remaining 1 cup all‑purpose flour to the bowl. Beat 2 minutes at medium speed, scraping the bowl occasionally, until a soft dough forms.

Using a rubber spatula, spread the dough evenly (it does not need to fill the corners perfectly) into the prepared 8 x 8‑inch pan. Cover with a towel and let rise in a warm place until doubled in size, about 30 to 45 minutes.

While the dough is rising, make the streusel: In a small bowl, stir together 1/3 cup all‑purpose flour, 1/3 cup sugar, 1/3 cup brown sugar, and 1 teaspoon Spice Islands® Ground Saigon Cinnamon. Cut in 1/4 cup butter or margarine with a pastry blender or two forks until the mixture is very crumbly but still has small visible pieces of butter. Stir in 1/2 cup mini chocolate chips.

When the dough has doubled, preheat the oven to 350°F. Sprinkle the streusel topping evenly over the risen dough.

Bake in the preheated 350°F oven for 35 to 45 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean or with only a few moist crumbs.

Remove the pan from the oven and cool slightly on a wire rack.

To make the frosting, in a small bowl combine 1 cup powdered sugar, 1 tablespoon milk, and 1/2 teaspoon Spice Islands® Pure Vanilla Extract. Stir and add up to 1 more tablespoon milk if needed to reach a slightly thin, drizzling consistency.

Drizzle the frosting over the warm (not hot) coffee cake. Let set a few minutes, slice, and serve.