In a medium saucepan, bring ½ cup water to a simmer over medium-low heat. Add the sugar and swirl the pan to combine. Increase the heat to medium-high and cook until a medium-brown caramel forms, about 12 minutes, occasionally swirling the pan to color the caramel evenly. Remove it from the heat and divide the caramel among eight (6-ounce) ramekins or silicone molds, swirling to make sure the bottoms and parts of the sides are fully coated.
Bring a kettle of water to a boil.
In a small bowl, whisk the coffee powder into the evaporated milk. In a large bowl, whisk together the eggs and sugar until the sugar is fully dissolved. Add the coffee-flavored evaporated milk, sweetened condensed milk, and vanilla and whisk to incorporate. Strain through a fine-mesh strainer into a large pitcher (this removes air bubbles).
Very slowly fill each ramekin about two-thirds full with the custard mixture. Place the ramekins in a shallow baking pan and place it in the oven. Carefully pour the boiling water into the pan to come halfway up the sides of the ramekins. Cover the pan with aluminum foil and bake for about 40 minutes, until the custards are just set and tremble in the center a little when shaken. Use tongs to carefully remove the custards from the water bath and place them on a wire rack to cool completely, about 30 minutes. Cover each one with plastic wrap and refrigerate them for at least 4 hours to chill (you can prepare the flans a day or two ahead).
To unmold the flans, place the molds in a pan with 1 inch of warm water for 5 minutes. Loosen the custard by running a sharp, thin knife around the inside of the ramekins and place a rimmed plate upside down on top of each. Invert the plates, carefully lift the ramekins off to remove them and reveal the caramel, and serve.
The best part about this dessert is that they can be made in advance and refrigerated and plated once your guests are ready for a sweet Mexican dessert they will never forget.