Ok....I am going to take a stab at this as I have a few guesses by your description.
If it is the taste more than a texture thing then I would ask if you know the two variants of cocoa powders? One is natural and the other dutched. From the description you had said that it had VERY distinctive chocolate flavour with the aroma of chocolate. That says to me that they could have been using a dutched variety of cocoa. They could have also roasted the cocoa powder more to accentuate the cocoa taste.
Natural cocoa powder (i.e.:Hershey's) is in an acidic form and the taste lends more citrus-like and slightly bitter to the taste. Dutched cocoa powder is more alkaline in form and smooth, rich and dark chocolate to the taste. Dutch process cocoa has a more intense "chocolatey" flavor while natural cocoa looks lighter in color and tastes slightly astringent.
Chocolate is naturally acidic, so natural cocoa powder typically has a pH between 5 and 6 (for context, water is 7, right in the middle). That acidity bears out in natural cocoa's flavor, which gives the cocoa a sharp, almost citrus fruit finish. Remember, that just like a chocolate bar, cocoa powder flavor varies by brand. While all natural cocoas will have certain characteristics in common (bitterness and astringency), flavors will vary based on the cacao bean and how it's manufactured. In most U.S supermarkets, natural cocoa is the most commonly available variety of cocoa—think Hershey's, Ghirardelli, and Scharffen Berger.
Dutch process cocoa powder (ie: Valrhona - also sometimes called "alkalized," "European style," or "Dutched") is washed with a potassium carbonate solution that neutralizes cocoa's acidity to a pH of 7. Although all cocoa powders can vary in color from light reddish brown to a richer dark brown, the Dutch process gives the powder a noticeably darker hue.
Dutch process cocoa has a smoother, more mellow flavor that's often associated with earthy, woodsy notes. There are also heavily Dutched "black" cocoa powders that bring the cocoa powder to an alkaline level of 8. This the kind of bittersweet cocoa you'll find in Oreo cookies.
Since Dutch process cocoa isn't acidic, it doesn't react with alkaline leaveners like baking soda to produce carbon dioxide. That's why recipes that use Dutch process cocoa are usually leavened by baking powder, which has a neutral pH.
Many recipes don't specify whether they call for natural or Dutch process cocoa, but American recipes tend to use natural, as that's what you'll find from most American supermarket brands. (Hershey's, for instance, is a natural cocoa.) When in doubt, stick to the leavening rule: recipes that rely on neutral-pH baking powder for leavening are best with similarly neutral pH Dutch process cocoa; those that are leavened by baking soda should stick to natural cocoa powder. If the recipe calls for both baking powder and baking soda, either will work, but it's best to stick to what the recipe calls for to get ideal results.
So a cake with Dutch process cocoa will be slightly darker and fudgier. The cake with natural cocoa powder produces a lighter final result with a slightly more open crumb structure.
So now when you experiment with finding your perfect 'worth every calorie' cake, it might be just a case of different cocoa to play with rather than technique. Also I would say that if you decide to use buttermilk again, use it in a recipe that calls for both baking soda and baking powder as the soda neutralizes the acidity in the buttermilk and the baking powder is left to rise the cake and leave the intense chocolate flavour of the dutched cocoa powder to show through.
Hope some of this helps and if you need some recipes just let me know