My mother used to make all sorts of desserts with peanut butter when I was growing up. Peanut butter pie was one of my favorites! She also made peanut butter fudge, peanut butter cake, peanut butter cookies, etc... Needless to say, we loved peanut butter!
In a large microwave safe bowl, stir together with a whisk the sugar, flour, and salt. Mix well, then add the egg yolks from separated eggs. Don't stir them in yet. (The bowl I use is a large glass measuring cup bowl with a pour spout.)
In a separate glass cup, pour the evaporated milk and then add enough whole milk to measure up to 4 cups. Add this to the flour/sugar mixture and mix together well with whisk.
Warm the peanut butter in the microwave for about a minute to make it soft and more liquified. Add to the milk and flour mixture. Whisk all together well until well incorporated.
In the meantime, preheat the oven to 375 degrees. Then poke holes in the unfrozen pie crust with a fork and place in the oven. Bake until light brown or done. Remove and let cool.
Place the pie filling ingredients in the microwave. Cook in the microwave for 6 minutes initially. Remove and whisk thoroughly. You will find thickened filling in the bottom and on the edges. Break them up with the whisk until smooth.
Return the filling to the microwave and cook another 4 minutes. Keep a check on it and make sure not getting too thick. Depending on your microwave, you may need to remove it sooner than 4 minutes. I remove mine every couple of minutes and whisk until the filling reaches a thick pudding consistency.(If you choose, you can cook the filling on top of the stove on low heat, stirring constantly until thickened. I like the microwave method because it is not as tiring and it won't scorch this way.)
Note: If your filling gets too thick, add a little water and whisk in thoroughly. Don't use milk.
Pour the thickened filling into the baked pie crust and set aside. You may have a little left over.
To make the meringue:
Make sure the egg whites are room temperature. Add the baking powder. Mix on high with an electric mixer until stiff peaks form. Still mixing on high, add the sugar. Continue to beat the whites until very stiff peaks form. (You should be able to turn the bowl upside down without the whites falling out.)
Cover the pie filling with the egg whites making sure that they touch the crust all the way around. Take the spatula or spoon and touch the whites with the back of the spoon and lift quickly to form pretty little peaks.
Place the pie on a cookie sheet and put in the oven at 375 degrees. Leave until the meringue is as brown as you like. Some people like it golden with dark peaks. Watch it closely as to not burn the peaks.
Remove pie from the oven and allow to cool before slicing. We like it warm or room temperature when its fresh. Needs to be refrigerated after that. It's great cold, too!