Preheat oven to 350 degrees F. Combine the crushed gingersnaps, melted butter, and egg white in a medium bowl and mix well with a fork. Let sit for 5 minutes. Press the mixture into a 9-inch pie pan, using your fingers to smooth it and evenly cover the bottom and sides. Bake for 5 minutes. Check the crust, smooth the edges up if they are sagging, and bake for 5 minutes longer.
While the crust is baking, combine the flour and ¼ cup of the half-and-half in a heavy saucepan to make the custard. Stir with a whisk until smooth. Put the pan over medium-low heat and add the remaining half-and-half in a thin stream, whisking constantly. Stir in the sugar and continue to cook, stirring constantly, until the mixture begins to thicken. Continue cooking and stirring, not letting it boil, until it is as thick as pudding. Add a tablespoon or two of hot mixture to the egg yolk, stir well, and add the egg yolk to the hot mixture. Continue to cook for a few more minutes. Remove from heat and stir in the ginger and vanilla. Let cool slightly. Pour the mixture into the baked crust and chill.
Arrange the sliced peaches over the custard. Melt the jam or jelly in a small saucepan and brush over the peaches. Chill for two to three hours and serve.