Mix sugar and cornstarch together in the top of a double boiler. Add the two cups of water. combine egg yolks with lemon juice and beat until well mixed. Add to the rest of the sugar mixture. Cook over boiling water until thick--- about 25 minutes ( I use a heavy cast aluminum pan with a low heat. I don;t like cooking with double boiler)

I stir conntinuously with a wire wisk until thickened. Turn heat off. Add butter, vinegar, and lemon extract and stir till thoroughly blended and butter is melted. Pour mixture into 9-inch pie shell and let cool. Cover with Meringue and brown in oven.

NEVER FAIL MERINGUE

4 tsps cornstarch(SURE-JELL- or Smart and final sells it under modified food starch label)
2 TBS cold water
1/2 cup boiling water
3 egg whites
6 TBS sugar
1 tsp vanilla
pinch of salt

Blend cornstarch and the 2 TBS of cold water in a sauce pan. Add boiling water and cook stirring until clear and thickened.
Let stand until COMPLETELY COLD.

With electric beater at high speed, beat egg whites until foamy. Gradually add sugar and beat until stiff but not dry. This is the part that was hardest for me cause you just have to use your own judgement. If the peaks stand straight up when you lift the beaters it is too much.

You want the peaks to lift up when you take the beaters out and then gentlyfold over on the tops. Kinda like a soft serve ice cream cone. Turn mixer to low speed, add salt and vanilla. Gradually beat in cold cornstarch mixture. Turn mixer to high again and beat well.
Spread meringue over cooled pie filling. Bake at 350* for 12 minutes or until top is browned.