Second , in order to maintain those little bubbles, you must know how to fold .
To fold successfully, you must have components that are rather alike in consistency and in temperature.
The following instructions are for right handed cooks. If you're left handed, just reverse them.
Try to use a bowl that rotates easily on your work surface.
Use one of those great large spoonulas - white rubber spatulas with a slight spoon like shape.
Have the components to be folded in the bowl. With your right hand, cut into the mixture with the side of the spoonula at the center of the bowl, all the way to the bottom. Then bring back the spoonula, through the mixture, to the surface, on the left side of the bowl, while at the same time, giving the bowl a counter clockwise quarter turn with your left hand. At this time, your grip on the spoonula should be loose, because the handle is completing a full turn. Do this manoeuver again and again.
It all sounds insane, but it is all very natural and easy. Basically, it is stirring on a vertical plane, as opposed to a horizontal plane: you help the components mix with each other whereas when you simply stir, you force them to.

4 eggs
2 tablespoons granulated sugar
1 cup Nestlé semi-sweet chocolate chips (6 oz)
1 and 1/3 cup heavy or whipping cream
1 teaspoon instant coffee
2 teaspoon Brandy or Whisky
2 tablespoons confectioners sugar

If this were a Chinese recipe, it would be called "Delight of Many Bowls". Make sure you actually own enough bowls to prepare this mousse.
Set a medium size metal bowl over a pan of simmering water. In this double boiler, combine the chocolate, half of the cream and the instant coffee, and stir occasionally until very very hot.
Meanwhile, separate you eggs. Whisk the yolks with the granulated sugar.
Carefully, pour a bit, say 1/3 cup, of hot chocolate cream into the yolks. Whisk well.
Then whisk the yolk mixture back into the chocolate cream, still on the double boiler.
Keep stirring or whisking non stop until the chocolate/cream/yolk mixture is very very hot.
Remove bowl from double boiler and mix in the liquor. 
Now the chocolate mixture needs to cool to just a tad warmer than room temperature. You may use the refrigerator, the freezer, an ice bath, or just patience, but in any case, do not overcool the mixture, as it would harden.
Now, beat the whites to a medium shape.
Then beat the remaining half of the cream with the confectioners sugar, to a medium shape as well. You may use beaters that are dirty with egg to whip cream, but not the other way around: even a trace of fat will prevent egg whites from whipping properly.
Now, scrape the chocolate mixture into your largest bowl.
Gently fold half of the whipped cream into the chocolate, not too thoroughly.
Then, gently fold half of the whipped whites into the chocolate, not too thoroughly.
Then, gently fold the remaining half of the whipped whites into the chocolate, not too thoroughly.
Finally, gently fold the remaining half of the whipped cream into the chocolate, until the color is even.
Using a Pyrex measuring cup, pour mousse into wine glasses or ramikins.
Refrigerate for three hours or overnight.

Cranberry Raspberry Mousse (about 5 servings)
This recipe is so popular, yet so easy, we're almost ashamed of it. It is egg-free.
Since it relies entirely on gelatin for setting, it is, technically, a Bavarian Cream (Bavaroise).

1 cup cranberry juice cocktail
1 box raspberry Jell-O
1  16oz can cranberry sauce
1 cup heavy or whipping cream

Bring cranberry juice to a full boil. Turn off fire.
Whisk in the Jell-O and dissolve patiently.
Whisk in the cranberry sauce.
Chill cranberry mixture in refrigerator until the sides start setting.
Whip the cream to a definite shape.
With your creamy beaters, whip the cranberry mixture, scraping the sides.
Gently fold the cranberry mixture and the cream together in a large bowl, until the color is almost even (a few streaks look pretty).
Using a Pyrex measuring cup, pour mousse into wine glasses or ramikins.
Refrigerate for three hours or overnight.