Set the oven to 350 °F and gather three 6 oz ramekins with a baking dish that accommodates them. The ramekins should sit flat without crowding.
Arrange the empty ramekins in the dish, pour water around them to a depth of 1 inch, then lift them out and transfer the water-filled dish to the oven. The bath will heat while you prepare the fillings.
Stir the pancake syrup with the blackstrap molasses, if using. The sauce should look evenly blended.
Divide the sauce evenly among the three ramekins. Each bottom should have a syrup layer.
Stir the cream, granulated sweetener, salt, and vanilla together in a medium bowl until the sweetener dissolves. The mixture should no longer feel gritty when stirred.
Break up the whole eggs and extra yolk with a whisk in a separate small bowl. The whites and yolks should form a uniform mixture.
Gradually introduce the egg mixture into the cream while whisking gently. Stop when the custard looks consistent, without separate egg streaks.
Spoon the custard over the syrup in equal portions, then carefully lower the filled ramekins into the heated water bath. Syrup rising around the custard’s edges is normal.
Bake for 35–45 minutes, checking for a set surface with movement at the center. A gentle nudge should reveal a soft central wobble rather than liquid sloshing.
Leave the ramekins in the baking dish for 10 minutes after removing it from the oven. The delicate custard will begin to settle as it cools.
Lift the ramekins from the bath and refrigerate for at least 2 hours. Chilling gives the custard the firmness needed for unmolding.
Trace a thin knife around the inside wall of each ramekin when ready to serve. Keep the blade close to the dish to preserve the custard’s sides.
Cover each ramekin with a plate and turn the pair over together. The ramekin should now sit upside down on the plate.
Give the inverted ramekin a gentle jiggle, then lift it away once the flan releases and serve cold. The sauce should pool around the custard.