what are the mini french sponge cakes that look like shells called ?!

They are Madelines and I don't think that they are Spongecakes. The flavor, taste and texture is more like a petite Pound cake than anything else.You can get them at Starbucks's and i have found them in our Safeway stores sold in a box of 8; that I finished in one day!!!

Heidi Swanson who write recipes on her site, 101 Cookbooks, has a wonderful recipe for Madelines.

Madeleine Recipe
Lanha and I both prefer metal pans to the newer silicon molds. My metal pan brings a beautiful golden hue to the cookies, and to be honest I don't like the looks of the silicon molds - all those zany colors. Madeleines look better baking in metal, I promise.

1 1/2 sticks unsalted butter (6 ounces)
2 tablespoons softened unsalted butter (for greasing pan)
3/4 cups unbleached all-purpose flour
4 large eggs
a pinch fine-grain sea salt
2/3 cups sugar
zest of one large lemon
1 teaspoon vanilla extract
powdered sugar

a bit of extra flour for dusting baking pan

Special equipment: A madeleine baking pan, regular or small

Preheat oven to 350 degrees Fahrenheit.

Melt the 1 1/2 sticks of butter in a small pot over medium heat until it's brown and gives off a deliciously nutty aroma, roughly 20 minutes. Strain (using a paper towel over a mesh strainer) - you want to leave the solids behind. Cool the butter to room temperature. By doing the butter first you can complete the rest of the steps while it is cooling.

While the melted butter is cooling, use the remaining 2 tablespoons of butter to grease the madeleine molds - get in there and make sure you get in all the ridges. Dust with flour and invert the pan tapping out any excess flour. Lanha uses "cooking spray" with flour to simplify this part.

Put the eggs with the salt in the bowl of an electric mixer with a whisk attachment. Whip on high speed until thick - you are looking for the eggs to roughly double or triple in volume - approximately 3 minutes. Continuing to mix on high speed, slowly add the sugar in a steady stream. Whip for 2 minutes or until mixture is thick and ribbony. Now with a spatula fold in the lemon zest and vanilla (just until mixed).

Sprinkle the flour on top of the egg batter, and gently fold in. Now fold in the butter mixture. Only stirring enough to bring everything together.

Spoon the batter into the molds, filling each mold 2/3 -3/4 full. I use a small cup filled with batter to keep things clean and manageable, it is easier than using a spoon.

Bake the madeleines for 12 - 14 minutes (7-10 minutes for smaller cookies), or until the edges of the madeleines are golden brown. Remove from oven and unmold immediately. Cool on racks and dust with powdered sugar.

Makes 2 -3 dozen regular madeleines.

Heidi Swanson's 101 Cookbooks

madelaines, they are sponge cakes, with a lot of butter.
They're sometimes dipped half in plain chocolate. They also use almond essence in them.

They are called Madelines.