If you are aroused by just the thought of chocolate, then the Big "O" ($5.25) at The Dessert Gallery (3200 Kirby, 713-522-9999) was created especially for you. The "O" stands for Oreos, which not only adorn the top of a three-inch-tall hunk of cake but are also crushed into the filling of white and dark chocolate mousse. As my fork penetrated the hard top layer of chocolate, gently slipping through the filling, I could feel the passion begin to swell. My knees were shaking with excitement. Should I nibble it around the edges or just go for it? I decided to start slowly, but mouthful by mouthful, the pace quickened. I bit into the Oreo on top of the cake (which was dipped in white and dark chocolate and decorated to look like a tuxedo), closed my eyes momentarily and moaned with pleasure. Thank goodness no one was watching.