Thank you so much for your reply; I did use 100% cacao powder... but there was milk in the cake as well...
The type of cocoa powder, ratio of cocoa powder to flour, and mixing method all influence the flavor of the cake.
Type: Natural cocoa powder imparts slightly more chocolate flavor. It produces a lighter color, and one that’s more reddish. Dutch processed has a more delicate flavor, but significantly deeper brown color. While I like the look of a Dutch cocoa cake, I prefer the flavor of natural cocoa powder. The brands I prefer are Hershey natural Cocoa or Callebaut natural. Callebaut is only available in restaurant supply stores or online.
Some bakers are reluctant to use Hershey, equating price with quality. But in this case, the cheaper Hershey natural cocoa produces excellent chocolate flavor.
Ratios: I find most recipes call for too little cocoa powder. Ingredient measurement sites like Tradition Oven, state 1 cup cocoa powder weighs approx 118g. Others state 1 cup cocoa = 100g. Where they came up with these weights is beyond me. I’ve measured (stir, spoon, level) and weighed cup after cup of cocoa powder; I come up with an average of 1 cup = 85g. So keep that in mind as ratio to flour is important in achieving chocolate flavor. More on that below.
Depending on the volume measurement method used, all purpose (AP) flour weighs 120g - 145g per cup. If you bake by volume, for consistency I’d recommend you use the spoon and level method.
Stir, spoon, and level:
1 cup flour = 120g flour
1 cup cocoa powder = 85g.
Most recipe use too little cocoa powder. While personal taste preferences vary, I find 30% cocoa powder to AP flour at a minimum is needed to produce a decent chocolate flavor. Most recipes are 25% or less; not enough to produce the chocolate flavor I prefer. So in developing your recipe, keep the weight of flour and cocoa powder in mind.
Method: blooming the cocoa powder in hot water produces a richer chocolate flavor than cocoa powder that’s sifted into the dry ingredients. A lot of recipe simply add hot water to the dry ingredients. I find this ineffective in developing chocolate flavor. The flour and sugar end up competing with the cocoa powder for the water. To bloom for maximum chocolate flavor, substitute half the milk with hot water. Mix the hot water into the cocoa powder and let it sit at least 15 minutes. Mix the cocoa paste into the creamed butter and sugar. If it’s an oil based cake, then add to the oil and egg mixture.
Flavor enhancer: since you used ground coffee you know coffee enhances the flavor of chocolate. But ground coffee won’t produce the effect as it’s not concentrated. Further, ground coffee will not dissolve. Use a powdered form of coffee. And not just instant coffee. Use espresso powder. Espresso powder is made from dark roasted coffee beans. Dark roast coffee beans are far more flavorful. The beans are ground and brewed; the coffee is then dehydrated. This produces a very concentrated coffee powder.
In the US, it’s available in most grocery stores. I just mix 1 - 1 1/2 teaspoons espresso powder into the hot water before blooming the cocoa powder in it.
Espresso powder is finer than instant coffee. While that doesn’t makes any difference when it’s dissolved, it matters when using in frosting. Ground coffee won’t dissolve. And instant coffee is coarse enough to be gritty.
As an aside, when I am asked to make a mocha cake I always inform the recipient of the fact that coffee is in the cake and/or icing. Some parents do not want their children to consume baked goods with the added stimulant from coffee. My brother and SIL are such parents. So when making chocolate cake or cupcakes for them, I bake a separate coffee free batch for my niece.
Double chocolate: you can achieve a richer chocolate flavor by combing cocoa powder and dark chocolate. Bittersweet is my preference, but semisweet works well. Melt 2 to 3 oz of chocolate, cool a bit then add to creamed butter or oil egg mixture with the bloomed cocoa powder paste. If adding melted chocolate, you do not need to reduce the amount of cocoa powder. You can add more melted chocolate if you like, just be aware the more melted chocolate, the denser the crumb.
Flour: flour and cocoa powder are both highly hygroscopic (pull water from environment). So flour and cocoa powder will compete for the water in the batter. Unbleached flour with a higher protein, such as King Arthur AP flour, has a higher absorbency rate than a bleached flour with a lower protein content. If using unbleached flour, it’s best to bloom the cocoa powder separately in hot water. You may also need to increase the over all liquid to counter the extra absorption rate of unbleached flour.