Add the sugar and water to a small saucepan. Cook over medium heat without stirring. Once it starts to bubble, increase the heat slightly and watch closely. When the syrup turns deep golden, remove it from the heat. Stir in the instant espresso and swirl to combine. Quickly pour the caramel into the bottoms of four ramekins, tilting each to coat the base evenly. Set aside.

Lightly beat the eggs in a bowl. Slowly pour the warm milk mixture into the eggs while stirring constantly to avoid curdling. Add the vanilla and mix well.

In a separate saucepan, combine the milk and sweetened condensed milk. Warm over medium-low heat, stirring occasionally, until fully combined and just hot. Don’t let it boil. Remove from heat and let it cool for a few minutes.

Pour the mixture through a fine sieve to remove any egg solids. Divide the custard evenly between the prepared ramekins.

Place the ramekins in a steamer over gently simmering water. Cover and steam over low heat for 30 to 40 minutes, or until a toothpick inserted into the center comes out clean.

Carefully remove the ramekins from the steamer. Let them cool to room temperature, then cover and refrigerate for several hours or overnight.

To serve, run a knife around the edge of each flan and invert onto a small plate. The caramel will flow over the top like a sauce.