Preparation

• Bake the puff pastry shells according to package directions until golden brown and puffed. Use the tip of a small knife to lift off the lids; discard them or save for another use. If the interior of the shells is still a little raw, lightly scrape out the uncooked pastry using the tines of a fork. Set the shells aside.
• In a heavy-duty 12-inch skillet, cook the bacon over medium heat, stirring often, until crisp, about 10 minutes; drain on paper towels. Transfer the bacon fat from the skillet to a heat-proof measuring cup; if you don’t have 1/2 cup of fat, make up the balance with melted butter. Reserve the skillet.
• Strain the oysters through a fine-mesh sieve set over a medium bowl to catch the oyster liquor. Measure 2 cups of the liquor; if you don’t have 2 cups, make up the balance with cold water. Set aside.
• In the reserved skillet, heat the 1/2 cup bacon fat over medium-high heat until hot, about 1 minute. Add the onions and garlic, and cook, stirring often, until the onions are soft and barely browned, about 3 minutes. Add the flour, whisking to blend thoroughly. Continue cooking, whisking constantly, until the flour is a very light brown, about 1-1/2 minutes. Whisk in the oyster liquor and cream. Bring to a boil over high heat, whisking constantly and scraping the bottom and sides of the skillet as you go, about 1-1/2 minutes.
• Add the drained oysters, bacon, parsley, sage, cayenne, and 1/2 tsp. black pepper. Turn the heat down to low and cook, stirring, just until the edges of the oysters curl, about 2 minutes; do not overcook. Remove from the heat and season to taste with salt.
• To serve, divide the puff pastry shells among 12 warm, small, wide bowls (or put them onto a warm large platter). Fill the shells with the oyster mixture, and then spoon the remaining oyster mixture around the shells. Garnish each with a pinch of scallion.