I read about this chocolate mousse on Cafe Fernando in December, but knowing that Valentine's Day comes on a Monday this year, I've been waiting to tell you about it until now. This mousse is so fast and simple that you can and should make it for your Valentine, even if it's been a really long day and cooking is the farthest thing from your mind.
The technique is very cool. You simply melt chocolate in some water, and then whisk the bejeezus out of it over an ice bath until it cools and thickens into ready-to-eat chocolate mousse. When I tried it, this only took about 3 minutes of whisking.
In the blog post, there's a link to a video of Heston Blumenthal demo-ing this recipe. It's worth watching for an explanation of what's happening at the molecular level as you whisk, plus you'll get to see what the mousse should look like when it's ready—helpful for avoiding overwhisking.
One thing to keep in mind: Because the mousse is essentially 70% bittersweet chocolate, it might be a bit intense for some, but you can sweeten it, and you can also add liqueur or other flavorings to dress it up as you like.