Yes, you can enjoy flan on a low-cal diet. The secret to eating it--or any other dessert while dieting--is portion control.
Let's be realistic. You cannot eat half a pie and lose weight. Same goes for cake or flan. But you can indulge your sweet tooth in moderation taking care to account for the fat and calories in your daily plan.
A 300-calorie piece of cake will require that you walk for 30-60 minutes, depending upon your speed and the level of the ground. So, keep that in mind when you are thinking about the dessert cart.
Better yet, split your dessert with a friend. You both get to enjoy it and the calories and fat are cut in half for you both!