For the custard:

First, soak raisins in hot water to cover for at least an hour up to four hours. Drain very well, reserving the raisins and discarding the water.

In a large saucepan stir together 1 1/4 cups granulated sugar and the flour. Add sour cream but do not stir yet. Separate eggs. Reserve the three whites for meringue. Add the yolks to the saucepan. Add the vanilla. Stir mixture together. Stir in the raisins.

Cook over medium heat, constantly stirring until the mixture is thick and bubbly. Turn off the heat, place a film of plastic wrap directly on top of filling to help hold in the heat, and cover with a lid.

For the meringue:

Mix together sugar and cream of tartar, set aside.

In a small saucepan, add the tablespoon of cornstarch, then whisk in 1/3 cup water. Bring to a bare simmer and cook, whisking occasionally, until it becomes just thickened and translucent looking, 1 to 2 minutes at most. Remove from heat, transfer to a small bowl (so it doesn’t continue to cook from the heat of the pan) and let cool slightly to barely lukewarm as the eggs are being whisked.

If using stand mixer, fit it with the whisk. Beat egg whites and vanilla at medium-low speed until foamy and frothy. Turn the speed up to medium-high and add, a tablespoon at a time, the cream of tartar and sugar mixture. Beat until incorporated (it won’t feel grainy when you run a bit between your fingers) and the mixture forms soft, billowy mounds.

While continuing to whip, add the cooked cornstarch mixture, about a tablespoon at a time. As it’s added, place it between the beaters and the side of the bowl. Continue to beat until stiff, glossy peaks form, about two to three minutes longer.

Assemble:

If filling is not still hot, during the last minutes of whipping the egg whites, remove plastic and return to very low heat for just a minute or two to warm. Working very quickly, spread the warm raisin filling mixture into the pre-baked pie crust. Smooth it out.

Still working quickly, using rubber spatula, immediately distribute dollops of meringue evenly around edge first and then the then center of pie, attaching meringue to pie crust to prevent shrinking. Top off with any remaining meringue. Use the back of spoon to create attractive swirls and peaks in the meringue.

Bake at 350°F for 20 minutes. (Always check early, ovens vary.) Cool at room temperature for up to 3 hours then chill for at least 1 hour before serving. Serve chilled or at room temperature.