Baking – cake smells bad of egg, is dense and rubbery

My sponge cake recipe has the same thing (though I think it has 1/2 dl water). It's basically because the person creating the recipe found that without it the cake batter was too thick and didn't yield a cake that was airy enough. When I left out the water, the cake became more dense and didn't rise quite as much. I find that that water is a nice place to add various flavours, like lemon juice or coffee by substituting some of the water.

I'm not sure I see any major benefit in creaming the sugar with the egg yolk here. And it's not going to produce a "creamy" texture in your batter: beating yolks with sugar is generally about lightness and/or to ensure eggs don't "clump" when cooked. You will achieve both of those goals more effectively by (1) beating the egg whites, and (2) thoroughly mixing the egg yolk into the other liquid ingredients.

Most pancake recipes use the so-called "muffin method" of combining ingredients:

• mix together all wet ingredients in one bowl
• mix together all dry ingredients in another bowl
• make a "well" in the middle of the dry ingredients to maximize surface contact when you pour the wet into the dry
• add wet ingredients to dry ingredients all at once
• whisk just briefly until the ingredients are barely combined and still often a little "lumpy" (this avoids gluten formation and toughness which can happen with more beating, as well as preserving a few "lumps" of leavening powder in some cases where moisture is the main activator for rising)
• if the eggs are separated and the whites beaten for extra lift, the whites are folded in gently and quickly at the end

I have used variations of this sort of method for many pancake recipes. I generally just add the (beaten) egg yolk to the rest of the wet ingredients.

If you were making a sabayon (zabaglione), you usually whip the egg yolks with sugar until the ribbon stage (or past) by introducing heat, which greatly speeds up the process and allows the sugar to dissolve more thoroughly. But the point generally isn't to dissolve the sugar; it's to break up the egg so it won't be grainy when cooked. It also creates a relatively stable mixture -- when you suddenly add a bunch of liquid to it (as in your recipe), it will break up and you'll likely lose quite a bit of "lift."

It's true that beating can add some lightness to the yolk mixture, but in the case of something like pancakes, I can't imagine this will produce a significant effect once the yolks are combined with the rest of the wet ingredients and then mixed into the batter. Beating the egg whites for a few minutes will have a much, much greater effect on the lightness of your pancakes than if you whipped your yolks for an hour. (If you had a recipe which had a significant amount of yolks, I suppose it might be justified in some cases.)

Lastly, I've never personally had a problem with sugar dissolving in pancake batter. But if that's your problem -- I'd think dissolving the sugar in a larger quantity of liquid (e.g., the milk) will be more effective than creaming it with a tiny amount of egg yolk.

You also mention butter cakes. Almost all butter cake recipes I can recall usually involve creaming the butter with the sugar and then adding eggs (whole eggs or just yolks). That's a very different process than what you're doing here. In the case of butter cakes, you generally want to cream the butter and sugar until it's no longer grainy -- even before adding eggs. So I'm not really certain what the problem might be there.