Bring water to boil in a large pot. Boil tomatoes for about 10 seconds. Peel tomatoes and slice.
Layer tomato slices, scallion and basil in individual (8 oz) ramekin. In a small cup, combine the mayonnaise, lemon juice, salt, sugar and pepper. Pour over the tomatoes. Bake for 20 minutes. Drain juice. Pour cheddar cheese. Brush puff pastry sheet with egg wash (egg and milk) and cut it in 1 inch strips. Lay the strips on top of the cheese. Bake another 20 minutes or until the pastry is golden brown.