Step 1: Preheat the Oven

Preheat your oven to 325°F (160°C). This moderate temperature ensures gentle cooking, preventing the flan from curdling.

Step 2: Prepare the Caramel

1. In a medium saucepan over medium heat, melt the granulated sugar, stirring continuously.
2. The sugar will slowly dissolve and turn into a golden-brown caramel. Be patient and avoid stirring too aggressively, as this can cause crystallization.
3. Once the caramel reaches a rich amber color, immediately pour it into the bottom of a greased muffin tin, ensuring each muffin cup gets an even layer.
4. Work quickly, as caramel hardens fast.

Step 3: Make the Custard Mixture

1. In a large mixing bowl, whisk together eggs, whole milk, sweetened condensed milk, vanilla extract, and salt until fully combined.
2. For an ultra-smooth texture, strain the mixture through a fine-mesh sieve to remove any egg solids.

Step 4: Fill the Muffin Tin

1. Carefully pour the custard mixture over the hardened caramel in each muffin cup, filling about three-quarters full.

Step 5: Prepare a Water Bath (Bain-Marie)

1. Place the muffin tin in a larger baking dish.
2. Pour hot water into the baking dish until it reaches about halfway up the sides of the muffin tin.
3. This step is crucial as it ensures even baking and a creamy texture, preventing cracks.

Step 6: Bake the Flan Muffins

1. Transfer the baking dish to the preheated oven.
2. Bake for 45-50 minutes or until the custard is set but still has a slight jiggle in the center.
3. To test for doneness, insert a toothpick into the center—it should come out mostly clean with a slight residue.

Step 7: Cool and Refrigerate

1. Remove the muffin tin from the oven and let it cool in the water bath for about 15 minutes.
2. Once cooled, transfer the tin to the refrigerator and chill for at least 2 hours, or overnight for best results.

Step 8: Unmold and Serve

1. Run a knife around the edges of each flan muffin to loosen it.
2. Carefully invert the muffins onto a plate. The caramel will drizzle over the top, creating a beautiful, glossy finish.