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1
Preheat the oven to 350u00b0 Fahrenheit and butter a 9 inch by 13 inch baking pan.
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2
Begin with the streusel. Melt the butter in a small bowl and set aside to cool.
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3
Combine the sugar, flour, cinnamon, salt, and vanilla in a small bowl, and pour the cooled butter on top.
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4
Mix with a fork until thoroughly combined, and large chunks remain. Set aside while you work on the cake.
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5
Sift together the flours, baking powder, cinnamon, and salt in a medium sized bowl and set aside.
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6
In another medium sized bowl, add the bananas, eggs, Greek yogurt, and vanilla. Set aside.
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7
Using a hand mixer set to the highest speed, cream the butter and sugars in a large bowl until very light in both color and texture, about two to three minutes.
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8
Using the same blades, use the hand mixer to beat all of the wet ingredients together until homogenous. It may be a little chunky!
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9
Add the banana mixture to the butter mixture, beating until smooth and fluffy, another two minutes.
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10
Add half of the dry ingredients and beat until no ribbons of flour remain. Add in the other half and beat until completely combined. The batter will be thick!
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11
Pour the batter into your greased pan. Bake on the middle rack for 20 minutes.
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12
Pull the cake from the oven and sprinkle your reserved streusel on top, gently pressing it into the very top of the cake. Return the cake to the oven and continue baking until a toothpick comes out clean and the cake springs back when touched, about another 22 to 25 minutes.
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13
Move the cake to the top rack of the oven and set the oven setting to broil. If your oven doesn't have this setting, turn up the temperature to 450u00b0 Fahrenheit. Broil for 30 seconds to a minute. This gives the coffee cake a crunchy streusel topping.
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14
Remove from the oven and let cool completely. Cut into 16 servings and dust with powdered sugar.
