Place milk, cream, salt, sugar, salt and ground coffee in a sauce pan. Heat on medium until the sugar is dissolved and the mixture is about to simmer (do not let it boil). Take the pan off the heat and let the coffee steep for 10 minutes.
In the meantime, Add in the eggs and vanilla extract in a medium bowl. Whisk lightly.
Bring 4-5 cups of water to the boil (enough to create 1-inch depth in the pan).
After 10 minutes of steeping, strain the coffee mixture. Then, gradually add it to the eggs while whisking. Do not add more than a little at a time or the eggs will be cooked and chunky.
Strain the mixture to remove the coffee grounds. Pour it into a pitcher or a liquid measuring cup or any sprouted container so it's easier to pour into the ramekins.
Divide the custard between the ramekins. Pour the boiling water in the pan until it comes halfway up the sides of the ramekins.
Carefully, place the pan in the preheated oven and bake for about 30 minutes, until the sides are set but the center is slightly jiggly!
Let the ramekins cool down on a wire rack for 30 minutes, then refrigerate them for 4-8 hours. Overnight is better.
When ready to serve, take flat knife and run it around the flan to loosen. Invert the flan onto your serving plate. You may need to shake the ramekin to get the flan out.