How to Make It
In a food processor, pulse the flour, cornmeal, baking powder, sugar and salt. Add the butter and pulse until it's the size of small peas. Add the half-and-half and pulse just until the dough comes together. Transfer the dough to a lightly floured work surface and knead 2 or 3 times. Flatten the dough slightly and roll it out to a 10-inch square. Cut the dough into 2-inch squares and refrigerate on a baking sheet.
In a large pot, cook the bacon over moderate heat until golden and the bacon fat is rendered, about 8 minutes. Using a slotted spoon, transfer the bacon to a plate. Discard all but 1 tablespoon of fat from the pot. Add the onion and garlic and cook over moderate heat, stirring, until softened, 6 minutes. Add the bacon, andouille and 3 cups of the Turkey Stock and bring to a boil over high heat. Add the collards in 3 batches, stirring so each batch wilts before adding more. Cover and simmer over low heat until the collards are very tender, 30 minutes.
Preheat the oven to 375°. Add 1 cup of the half-and-half and the remaining 1 cup of stock to the collards and bring to a boil. Stir the cornstarch slurry and add it to the pot. Cook, stirring, until thickened, 2 to 3 minutes. Season with salt and pepper.
Transfer the collards to a large ceramic or glass baking dish. Top with the biscuit squares, overlapping them slightly, and brush the tops with the remaining 2 tablespoons of half-and-half. Season the biscuits well with pepper and bake for 50 minutes, or until the greens are bubbling and the biscuits are golden. Let rest for 20 minutes before serving.