1Preheat oven to 350 degrees F (175 degrees C). Grease 6 (4-ounce) ramekins.
2Slowly melt sugar in a large skillet over low heat, stirring constantly, until browned but not scorched, about 8 minutes. Divide caramel equally among the ramekins and allow to cool.
3Combine whole milk, coconut milk, evaporated milk, sweetened condensed milk, and vanilla extract in a saucepan over low heat. Stir continuously until it begins to steam, about 5 minutes.
4Whisk 3 eggs together in a bowl; slowly pour beaten eggs into the warm milk mixture, whisking constantly until the custard is combined.
5Place ramekins in a casserole dish and fill with boiling water to reach halfway up the sides of the ramekins. Divide custard evenly among ramekins, over the caramel sauce, about 1/2 inch from the top. Cover casserole dish tightly with foil. Bake in the preheated oven until the custard is set, about 1 hour. A knife gently inserted into the center of a flan should come out clean.
6Remove ramekins from the water bath and allow to cool to room temperature. Refrigerate for 2 to 3 hours before serving to chill completely. Run the tip of a paring knife around the edges to release the flan. Place a plate over the top of the ramekin and flip to release the flan onto the plate, caramel side up.
Footnotes
Tip
Aluminum foil can be used to keep food moist, cook it evenly, and make clean-up easier.