To make the filling, in a saucepot, whisk together the egg yolks, milk, sugar, flour, and salt. While stirring, cook on medium heat until it bubbles and thickens, about 5 to 10 minutes.
Remove from the heat and stir in the vanilla, cinnamon, cayenne, and peanut butter until well combined.
Meanwhile, poke holes in the piecrust with a fork and bake until it’s brown, about 20 minutes.
To make the meringue, beat the egg whites with salt and when they start to get fluffy add the sugar.
Pour the peanut butter custard into the baked pie shell and top with the beaten egg whites. Bake pie until peaks on the meringue are lightly browned, about 10 minutes.