Preheat oven to 450°F. Arrange 4 (4 oz) ramekins on a baking sheet. Generously coat insides with the baking spray.
Finely chop the chocolate and add to a large microwave-safe bowl, along with the butter. Microwave in 30-sec. intervals until butter is melted. Stir until chocolate is smooth.
To a medium mixing bowl, add 2 eggs. Separate remaining 2 eggs, adding only yolks to mixing bowl (discard the whites). Add the sugar and salt. With a hand mixer, beat until smooth and thickened. Add egg mixture to chocolate mixture, along with the flour. Stir until well combined and divide among ramekins.
Bake 8–10 min., until top is just set but centers jiggle when shaken. Let stand 5 min. Run tip of paring knife around edges to release from sides of ramekins.
Cover top of each ramekin with a small serving plate and turn over. Let stand 15 sec. before removing ramekin. Serve warm topped with some ice cream.