How do you convert a cake recipe to make brownies? I'm wondering how to convert a cake recipe to make brownies. My intention is to use this recipe for Mexican Chocolate Cake With Mascarpone Frosting. The cake part calls for the following ingredients:

1 cup unsweetened cocoa
2 3/4 cups flour
1 1/4 cups sugar
1 cup packed brown sugar
1 1/2 Tablespoon cinnamon
2 teaspoons baking soda
1/2 teaspoon cayenne pepper
1/2 teaspoon salt
2 cups whole milk
1/2 cup olive oil
1/2 cup vegetable oil
2 eggs
2 Tablespoons balsamic vinegar
1 1/2 Tablespoons vanilla  

How can I convert that into a brownie recipe?

I'm thinking more oil/butter and less water would work, but I'm not sure of the ratios. I imagine I'd probably also cook brownies for a shorter amount of time. 

What determines a cake's fluffiness and a brownie's dense chocolatey awesomeness? Is there a general formula you can follow for converting cake to brownies? (Since this question is about conversion, I suppose it could also apply to a boxed cake mix in case I'm too lazy to go to the store.)
Brownies are typically dense and less fluffy compared to cake.  What you want to do is to make the cake recipe more dense to make it more like brownies. Here are a few factors that would effect density/fluffyness.


Number of eggs: Adding more eggs will make the cake more dense
Preparation of eggs:  Beating the eggs will cause the cake to be more fluffy since you are introducing more air into the mixture. You should stir them lightly with a fork (not beat/whisk them) until just liquefied, to avoid a fluffy cakelike texture. 
Addition of baking powder.  Most cake recipes call for baking powder while many brownie recipes do not.


I suggest reviewing some brownie recipes and the comments to get a feel for a good starting point for the cake recipe modifications.