Make the Shortbread Crust:

1. Add the quick oats, all-purpose flour, light brown sugar and salt to the bowl of a food processor. Process for 1-2 minutes, or until the oats break down into fine pieces.
2. Add in the butter and pulse 5 times.
3. With the motor running pour in the egg and let the dough process until the dough forms together into a cohesive ball around the blade, about 1 minute.
4. Scrape the dough from the bowl and place it in a 9” non-stick tart pan with a removable bottom.
5. Using a small offset spatula, smooth down the soft dough to an even layer, including up the sides.
6. Place in the freezer to harden while the oven preheats.
7. Preheat the oven to 375ºF.
8. Remove the tart pan from the freezer, and pierce holes into the bottom of the crust with a fork. Cut out a parchment paper circle and place it in the tart pan over the dough, taking care to push it into the edges of the pastry.
9. Add dry rice / beans or pie weights to the parchment, making sure to push the weights all the way to the edges.
10. Bake for 20 minutes, then remove from the oven and remove the parchment and pie weights. Return the pie crust to the oven and bake for an additional 5-10 minutes or until the crust is very dry and light golden brown. Lower the oven to 350ºF.

Make the Filling:

1. In a medium bowl, add the egg yolks, peanut butter, sugar and salt. Gently mix together (you don’t want to overwork the peanut butter) until just combined. Slowly whisk in the half and half, a little at a time, until it’s fully combined. Whisk in the vanilla.
2. Transfer the filling to the blind baked tart shell.
3. Bake the peanut butter tart in the middle rack for 20-30 minutes, or until the filling is set around the edges at least 2-½” in, and just barely wiggly in the middle.
4. Let cool completely, at least 4 hours, at room temperature.

Make the Fluff:

1. If you are using store-bought fluff, you can place it on just before serving.
2. To make the fluff, fill a small pot with at least 1 ½ inches of water and turn on the heat to medium-high. 
3. In a metal stand mixer bowl, combine the egg whites, salt, sugar, and cream of tartar and whisk together until fully combined.
4. Set the bowl over the steaming pot of water. Alternate between whisking the mixture and scraping down the sides of the bowl (so no sugar gets stuck to the sides and hardens) with a spatula, until egg whites reach a temperature at 160°F, roughly between 8 and 10 minutes. The mixture should be light and fluffy and be completely smooth with no granules of sugar remaining.
5. Transfer to a stand mixer fitted with a whisk attachment, whip on low speed for 1 minute, scraping down the sides with a clean spatula. Increasing the speed to medium and whip until the meringue is glossy and beginning to pull away from the sides and the bowl has cooled down significantly, about 8 minutes. Add in the optional vanilla extract and whip until combined.
6. Add the fluff to the top of the pie.
7. Serve immediately.