I am trying to make a warm drink using cocoa without much additions. Basically I boil water and the slowly add it to a cup with cocoa powder while I stir. I also add some cold milk. When I stir with a spoon, I see that it becomes sticky and liquid and looks like butter melted. The problem is that when I fill the cup with boiling water and some cold mild and start drinking it, in the end most of the cocoa powder have stayed stuck at the bottom of the cup. How can I make it so that it is completely dissolved but only using water and a bit of milk? Please note, that I don't have a microwave 
There are many different ways to mix ingredients, which will affect the final texture.  Here are a few that I'm familiar with, but I suspect a professional baker would know even more: Creaming : Beating the fat and sugar together first to encorporate air, then add your other ingredients.  Requires having a solid fat.  Typically used for cookies and some cakes. Muffin Method : Mixing the liquids and dry ingredients individually, then mixing the two together.  Typically used for quick breads (and muffins) Sponge: Whole eggs are whipped, then sugar and flour are added.  Used for pound cake.  (some argue that it's no longer a sponge if you add chemical leavener) Chiffon : Mix together everything but the egg whites.  Beat the egg whites, then fold them in.  Used for chiffon cakes.  (rather similar to making a souffle, but the proportions for cakes are different and includes chemical leaveners) Angel Food : Whip your egg whites, then slowly fold in the sugar, flour and other ingredients.  Used for angel food cake (and requires a special pan, so it's upside down as it cools).  Unlike other cakes, there are no egg yolks or other fat. Obviously, if you don't have a solid fat, you can't use the creaming method.  So an olive oil cake simply can't use the creaming method. Muffin method typically uses a liquid fat (there are variants that use fruit puree and no fat).  I'm not familiar with the "All at once" method, but I suspect that it would also use liquid fats. The only other solid fat methods that I'm aware of aren't used for cakes -- they're used for pie crusts, biscuits, and puff pastry. As for the question about "beat until smooth", it again depends on ingredients and desired texture -- you typically do not do this with cakes once flour has been added.  If you do, you'll develop gluten, which creates a chewy texture.  This might be okay for cookies or yeast breads, but it's a problem for cakes and muffins. If you over-beat a muffin, you'll get "tunneling", when bubbles are trapped inside the batter and end up looking like a worm has burrowed through the item.  This is why muffins, brownies, and pancake recipies often tell you to stir until "just combined" or even that few flour streaks are okay. 