Preheat your oven to 375 degrees F. Grease 10 ramekins or 1 9-inch round cake pan with cooking spray. Beat your eggs and set them aside.
In a heavy saucepan, cook ½ cup of the maple syrup over medium-high heat, until it reaches the hard-ball stage (260 degrees F). You will need to insert a candy thermometer in the pan to monitor the temperature. It should take at least five minutes to reach this stage.
Immediately and very carefully pour the syrup (it will be extremely hot) into your greased ramekins, trying to keep the amounts even. (The longer the syrup sits in the pan, the darker it will become until it burns.)
Place your flour in a medium mixing bowl. Gradually add your remaining 1 cup of maple syrup, whisking until blended. Add your milk, vanilla, eggs and salt. Beat with a mixer at low speed until well blended.
Pour the milk mixture into a measuring cup or something with a spout and evenly pour the mixture over the maple caramel in your ramekins. If using ramekins, fill 2 9x13 pans with one inch of hot water. Place the ramekins in your baking pans. (If you are using a round cake pan for the flan, you will need to add an inch of water to a large roasting pan and set your cake pan in it.)
Bake for 1 hour and 10 minutes, or until a knife inserted in the center comes out clean. Wearing gloves, take the ramekins out of the baking pan and set them on a wire rack to cool for an hour. Then, chill the flan in the refrigerator for two hours before serving.
To serve, invert a dessert plate over the top of a ramekin and flip over the flan onto the plate. Add blackberries, strawberries, or other berries as garnish. Only invert the servings you will need at the moment. Refrigerate leftovers for up to three days.