Preheat the oven to 325 degrees F.
In a heavy saucepan over medium heat, combine the 2/3 cup sugar and cornstarch. Add 1/4 cup water and whisk until smooth.
In a medium bowl, beat the egg yolks. Add the half-and-half, beating until combined. Gradually add the egg mixture to the cornstarch mixture in the saucepan, stirring constantly, until the mixture boils. Boil 1 minute, stirring constantly until thickened. Remove from the heat; stir in the vanilla. Add the peanut butter, stirring to combine.
Arrange half the chocolate wafers in the bottom of a 1 1/2-quart baking dish; spread half the pudding over the wafers. Arrange remaining wafers along the outside edge of the baking dish. Spread the remaining half of the pudding.
In a metal or glass bowl, beat the egg whites at high speed with a mixer until foamy. Add the cream of tartar and 1/4 cup sugar and beat the egg whites until the sugar dissolves and soft peaks form. Spread the meringue over the pudding, sealing to the edge of the dish. Bake until lightly browned, about 25 minutes. Let cool to room temperature before serving.