Preheat oven to 500°F. Fill a large bowl withboiling water.
Place a baking sheet over;dust with flour.
Place dough on bakingsheet; cover loosely with plastic wrap andlet sit for 10 minutes to soften. Flip dough;cover and let sit 10 minutes longer.
Meanwhile, drain clams, reserving liquid.Cook bacon in a 12" cast-iron skillet overmedium heat, stirring occasionally, untillightly browned, 4–5 minutes.
Transferbacon to a paper towel–lined plate.
Addgarlic and shallot to drippings in skillet andcook, stirring occasionally, until softened,about 2 minutes. Stir in chard and 1/2 cupreserved clam liquid and cook, stirring, untilchard is just wilted, about 2 minutes. Seasonto taste with salt and pepper. Stir in butter,vinegar, and as many clams as you'd like.
Transfer mixture to a medium bowl.
Wipe out skillet and heat over medium-highheat until very hot.
Roll out doughon a lightly floured surface to a 12" round.
Sprinkle skillet with cornmeal and transferdough to skillet.
Brush top of dough with oil.Cook, shaking pan occasionally and turningpan to avoid hot spots, until bottom ofdough is golden and crispy, 6–8 minutes.
Spread chard mixture over dough.
Bakeuntil crust is golden and cooked through,6–8 minutes. Scatter bacon and cheese over;cook just until cheese is melted, 2–3 minuteslonger.
Per serving: 349 calories, 11 g fat, 41 g carbohydrate