At culinary school, we spent one whole class period making bombes, and it was a wonderful experience, although I've noticed it's not polite to talk about that sort of thing in public.
People can't hear the silent "e" at the end of bombe, so one risks being labeled a terrorist. Thus, it becomes necessary to modify the word on each utterance... "pastry bombe" or "ice cream bombe" or "bombe cake" or something of the sort.
The bombe glacée is a traditional French confection made with a cake dome that encloses a mousse or ice cream center.
You don't see them that often, and that's a shame, because it's fairly easy to construct a bombe.
I find that the mousse variety holds up a bit longer at room temperature, but the ice cream bombe seems to make people (particularly small people) squeal with delight.
To get started, you'll need a cookie sheet or jelly roll pan with a raised edge and a large, deep metal or glass mixing bowl. (Mine is from K-Mart's affordable Martha Stewart line)
The construction of a basic bombe works like this:
1. Bake a flat, flexible cake layer. (I used the chocolate genoise recipe for this.)
2. Cool the cake and and cut into pieces/strips.
3. Line the metal mixing bowl with plastic wrap and then line with the cake pieces, cutting smaller shapes (as necessary) to fit in all the spaces and make a single, uniform layer. This process is like making a cake puzzle across the inside of the bowl.
4. Pack mousse or softened (but not melted) ice cream into the empty space atop the cake, cover the entire bowl with plastic wrap or parchment and freeze 5 hours (or overnight).
5. Optional: Cover exposed ice cream top (cake bottom) with a quick chocolate ganache and let harden for 30 minutes in the freezer. This is just to seal up the bottom, but it doesn't show, and it's not necessary.
6. Using the plastic wrap lining for leverage, invert the bombe on a platter and quickly frost or ice it and/or decorate it. Return the bombe the freezer until it's time to cut and serve.
To illustrate, here's a bombe, still in the chilled bowl with the hardened ganache spread across the top.
Observe the inverted, undecorated bombe here (you'll note the white ice cream crevices where the cake pieces fit together).
And the frosted bombe here...
The lovely Suzy Hotrod kindly documented the before and after bombe photos, so toques off to her for making this funny little cake look professional.
I do recommend avoiding the lowfat ice creams for this project. They're often very airy and whipped, making them melt too quickly for use here. But that aside, you can really use whatever ice cream you like. I went with plain old vanilla but most anything you enjoy will work fine.