In a medium bowl, beat the yolks with 6 tablespoons of the sugar until pale and thick (about 5 minutes). In a medium saucepan scald the milk with 1 of the vanilla beans. Split vanilla bean. Beat the milk very gradually into the egg mixture. Return the mixture to the pan and cook, stirring constantly with a wooden spoon, for about 10 minutes, until the custard thickens enough to coat the back of the spoon. (Be careful not to let the mixture boil or the eggs will curdle). Remove vanilla bean. Place the pan over ice and stir occasionally to prevent a skin from forming.
While the custard is cooling, beat the whites with the salt, 4 tablespoons of the sugar, and 1/4 teaspoon cream of tartar until stiff peaks are formed.
In a 12-inch skillet, bring the water to a boil with the lemon juice. Lower the heat. Using a large kitchen spoon, carefully slide 8 scoops of meringue, one scoop at a time, into the simmering water. Poach the meringue for 1 1/2 minutes then turn over and poach for 2 minutes longer. Remove the meringues with a slotted spoon to a clean kitchen towel.
For the caramel syrup: Place sugar and water in saucepan and swirl (shake pan with circular motion) over moderately high heat until the sugar has dissolved completely. Then let the sugar boil, swirling the pan occasionally, until the syrup turns a light, nut brown. This will take 3 to 4 minutes. Remove saucepan from heat as soon as the desired color is reached; if you let it darken too much, it will have a bitter taste. Pour 1/3 cup of water into the preceding caramel and simmer, stirring, until the caramel has dissolved.
To assemble the dessert, pour the custard in a large serving bowl and float the meringues on top. Combine. Immediate drizzle the caramel syrup over the meringues and serve.