Chocolate brownies are cakey, dry and sad. Please help? (Healthy Baking Problems)

So, I've been trying to make healthier chocolate brownies, using a recipe from Amy's Healthy Baking. I've included the ingredients and recipe here.

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Ingredients

1 tablespoon canola oil

2 eggs

2 teaspoons vanilla extract (I used imitation, which is cheaper)

a pinch of salt

1/4 cup greke yhoghurt

1/2 cup sugar

5 tablespoons milk

3/4 cup unsweetened cocoa powder

1/4 teaspoon baking powder

3/4 cup whole wheat flour

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Its a one bowl recipe, so I just whisked everything together except the flour, where I used a wooden spoon. Even during the mixing process, the brownie batter was very thick and it was difficult to get it to pour into the bowl. The end result was cakey, not moist or fudgy like claimed. Any help would be appreciated. Thanks