Cook’s Illustrated reports that for the best chocolate flavor in desserts you should make a “pudding” by cooking cocoa powder with water, fat, and sugar, rather than mixing the cocoa powder into the dry ingredients. They say that “adding hot water to cocoa solids before incorporating them into the recipe causes a ‘blooming’ effect, enhancing the chocolate flavor in the final dish.” But adding sugar and fat increases this effect. This is because the sugar molecules bind more tightly to the water molecules, and the cocoa solids from the cocoa powder dissolve in the fat, which is a better carrier for cocoa flavor than water.
The specific instructions for making the “pudding” for a chocolate cake or other dessert:
Combine 4 ounces unsweetened chocolate, 1/4 cup cocoa powder, and 1/2 cup hot water in medium heatproof bowl; set bowl over saucepan containing 1 inch of simmering water and stir with rubber spatula until chocolate is melted, about 2 minutes. Add 1/2 cup sugar to chocolate mixture and stir until thick and glossy, 1 to 2 minutes. Remove bowl from heat and set aside to cool.