Lay a tea towel into a deep baking sheet and place 6 ramekins on top. Set aside.
Preheat oven to 325 F. (165. C) In a small sauce pan over MEDIUM heat, add 1 cup white granulated sugar and 3½ tablespoons water. Give it a little mix with a wooden spoon (only once) to make sure the water is evenly distributed. The caramel process should take about 10-11 minutes from when you turn on the heat to when you pour your caramel.
Again, do not mix sugar while it boils and bubbles. After 5-7 minutes you’ll start to notice the color changing and a smell of caramel. Let it continue to bubble without mixing for at least 2-4 more minutes.
When the sugar is starting to look like the color of warm mahogany, pick up your pan and give it a swirl. It will keep cooking once you remove the pan. Once color is right, pour evenly into the bottom of ramekins. (See detailed instructions in post to see exactly the correct color.)Note: If you don’t have a white pan to help you easily see the color, use a spoon to drip a few drops onto a white plate. In a medium mixing bowl, add 3 large eggs, 6 tablespoons brown sugar, 1 teaspoon pumpkin spice, ½ cup pumpkin puree and 1 tablespoon whisky (optional). Use a standing blender or immersion blender to combine. Blend for 1-2 full minutes. Set aside.
In a medium pot, add 1½ cups whole milk and 1 tablespoon vanilla extract. Turn your heat to MEDIUM. Heat for 3-5 minutes, or until a small amount of steam begins to rise, stirring occasionally.
Very slowly and steadily, pour egg mixture into heating vanilla milk, stirring/whisking the whole time you pour. If you don’t stir, the eggs may cook unevenly and get chunky. Once added, slowly stir for another 30 seconds. Remove from heat. Evenly pour pumpkin custard into ramekins, over the caramel.
Place pan in oven, and use a tea kettle to fill the pan half-way up the glasses with water (or you can fill the pan with water first and carefully place in the oven, but I find this to be a little tricky to do without spilling). Bake for 45 minutes to an hour until the edges of your flan are slightly brown.
Very carefully remove the pan and remove the ramekins with a towel or oven mitt. (Be careful not to spill hot water!) When they’re cool enough to touch, cover them with cellophane and place them in the fridge to set for a minimum of 5 hours. Ideally, 24 hours.