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Grease and flour a rectangular pan (9" X 13") and set aside.
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Preheat oven to 350 degrees F.
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Peel the ripe banana, place them in a bowl and mash them into a pulp with a fork.
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Set aside.
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In a separate bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, and salt. Set aside.
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In a stand mixer fitted with a whisk attachment, cream together the butter and brown sugar, beat in the vanilla extract. Whip for 2-3 minutes until the mixture becomes light in color. Stop the mixer and scrape down the sides of the bowl if needed to make sure all the batter is incorporated properly.
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Add the eggs one after the other, making sure each egg is fully incorporated into the batter before adding the next.
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Mix in the yogurt into the batter.
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Add the mashed bananas and mix thoroughly.
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Turn the mixer down to its lowest speed and add the flour in thirds combining it completely into the batter.
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Once the dry ingredients are combined into the batter, turn the mixer up to medium speed and give the batter a few more turns.
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Remove the bowl from the mixer and use a rubber spatula to fold in the raw hazelnut pieces.
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Transfer the batter to the bowl, smoothing the top over with a rubber spatula to make sure it is level. Add the hazelnut streusel to the top of the cake, making sure it is evenly placed over the top.
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Place the pan in the oven and bake for 50 minutes or until a knife inserted in the middle of the cake comes out clean.
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Remove from the oven and let cool in the pan. When the cake has cooled, remove it from the pan and place on a wire rack.
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Line a baking sheet with parchment paper and place the rack with the cake on top on the baking sheet.