In a saucepan, combine 100 g sugar, 30 ml water, and lemon juice for the caramel. Heat gently without stirring until it turns a deep golden color. Pour the hot caramel into the base of your flan mold, swirling to coat the bottom evenly. Let it set.
In another saucepan, combine 250 g sugar and 250 g water. Bring the mixture to a boil over medium heat until it reaches a temperature of about 221°F(105°C) to 223°F (106°C) to obtain a strand-like syrup. Let the syrup cool to room temperature.
In a mixing bowl, whisk together the egg yolks and whole egg until smooth. Gradually add the cooled syrup to the eggs, whisking gently to combine without creating foam. Strain the mixture through a fine sieve into the caramel-lined mold to ensure a smooth texture.
Cover the mold with foil and place it in a larger baking dish filled with hot water for a bain-marie. Bake at 356°F (180°C) or 320°F (160°C) for fan-forced for 40 minutes, or until just set and a toothpick comes out clean. Remove from the oven and let cool completely. Chill in the fridge for at least 6 hours or overnight.
To serve, run a knife around the edges and invert onto a plate to release the flan with the caramel on top.
Notes
Watch the Syrup Temperature: I always use a thermometer and stop cooking the syrup once it hits 221°F (105°C). That way, I get the perfect strand-like texture without overcooking it.Whisk Gently, Not Vigorously: I whisk just enough to blend everything without creating bubbles. It keeps the flan smooth and free of foam.Strain for a Silky Texture: I like to strain the egg mixture before pouring it into the mold; it makes a big difference in how silky the flan turns out.Chill Overnight if You Can: I usually leave it in the fridge overnight. It sets perfectly and is so much easier to unmold the next day.