Chocolate and vanilla are generally perceived to be polar opposites. Nothing to do with one another. "That's so -- vanilla," you'd say about something flavorless or dull; but no one would dream of saying, under similar circumstances, "That's so chocolate."

And yet chocolate and vanilla can make beautiful music together. More than that, chocolate needs vanilla.

Once I was given a brownie by a friend who'd just made a batch. I bit it and was struck by how bland it was. My friend could tell by my expression that something was off. "I forgot the vanilla," she apologized.

Without vanilla, chocolate just doesn't taste as chocolaty. With vanilla, chocolate is able to be everything it ought to be.

Chocolate makers figured this out a long time ago. Read the ingredients on the label of any chocolate bar. You'll see either vanilla or vanillin (an extract of vanilla).

It's appropriate for chocolate and vanilla to go so well together. They have a great deal in common.

Both were brought to the awareness of the western world at the same time, in the early sixteenth century. Both require a labor-intensive process to move them from pretty products of tropical plants to the food we love. This process includes some of the same steps -- harvesting, leaving the harvest in hot, humid conditions for several days in order to bring the full flavor out, and drying the beans thoroughly.

Chocolate and vanilla also both have devastatingly edible scents, and both have been considered to have aphrodisiac qualities. And the Aztecs, some of the earliest consumers of both substances, ground vanilla to mix with their chocolate beverages.

The next time you make brownies or chocolate-chip cookies, try doubling the recipe's recommended amount of vanilla. It's a perfect way to amp the flavor of the chocolate without having to add any more of it. The cocoa taste will leap out at you almost before you take that first bite.

Add a bit of vanilla to your next cup of hot chocolate. Or have a treat at breakfast -- stir some vanilla into your oatmeal, then sprinkle it with mini chocolate chips or cocoa powder.

Or you could go all out and make a chocolate-vanilla cake. (You'll have to soften a bar of butter in advance for this. Also, preheat your oven to 375 degrees.)

Melt about six ounces of semi-sweet or bittersweet chocolate and set it aside to cool.

Meanwhile, stir and toss together one and a quarter cups of cake flour, a teaspoon of baking powder, and a quarter teaspoon salt in a small bowl.

In a large mixing bowl, beat the butter with ¾ cup granulated sugar for about five minutes, until light and fluffy. Beat in two eggs, one at a time, and two teaspoons pure vanilla, beating well after each addition.

Alternately add the flour mixture and one cup of whole or 2 percent milk to the butter mixture, beating thoroughly throughout the process.

Divide the batter in half -- you'll have about one and a half cups in each bowl. Stir the melted chocolate into one half. Into the other, add another teaspoon or two of vanilla and mix well.

Spoon first the chocolate batter and then the vanilla into a greased cake pan. Stir gingerly with a sharp knife just enough to swirl the two flavors together a bit -- you want just a bit of marble, not to combine the mixtures.

Bake the cake for about half an hour -- start checking at about twenty minutes, and don't take it out until a cake tester comes out clean. Let cool in the pan on a rack for ten minutes or so, then turn the cake out onto the rack. Try to resist the urge to eat it before it has cooled completely -- the texture will be better.

This cake is rich and pretty enough to serve unaccompanied. If you feel the need for something, you can dust it with a bit of confectioners' (powdered) sugar, or offer some heavy or whipped cream on the side.