Preheat oven to 325 degrees F. Spread peanuts on a small tray and toast in the oven, stirring often for about 16-18 minutes (I only needed 8-10 max), until light golden brown. Let cool, then coarsely chop.

Place flour in a medium bowl, and sift in the baking soda and baking powder and whisk together.

Place butter and peanut butter in the bowl of a stand mixer fitted with the paddle attachment. Turn to medium-low speed and cream the butters until they have the consistency of mayonnaise and holds a peak when the paddle is lifted.

Add the sugar and mix for about 2 minutes, until fluffy. Scrape down the sides and bottom of the bowl. Add the eggs and vanilla and mix on low speed for 15-20 seconds, until just combined. Scrap the bowl again. The mixture may look "broken", but this is fine (over-whipping the eggs could cause the cookies to expand too much during baking and then deflate).

Add the dry ingredients in 2 additions, mixing on low speed for 15-30 seconds after each, or until combined. Scrap the bowl to ensure no dry ingredients have settled at the bottom. Add the oats and pulse on low 10 times to combine. Add the chopped peanuts and pulse to combine.

Mound the dough on a large piece of plastic wrap. Form into a rectangle about 5-by-7 inches. Wrap in plastic wrap and refrigerate for at least 2 hours, or until firm. (The dough can be refrigerated for up to 2 days or frozen for 1 month).

Once firm, unwrap the dough and place between two pieces of parchment paper and roll out into a 1/4-inch thick sheet. If the dough softens, slide it (in the parchment) onto the back of a sheet pan and refrigerate until firm enough to cut.

Using a 3 1/4 inch round cutter (mine was just shy of 3 inches), cut 8 cookies. Arrange the cookies on a lined sheet pan. Put the trimmings back in the refrigerator until the dough is firm enough to roll again, then cut out 4 more cookies. Add them to the sheet pan. Wrap the sheet in plastic wrap and freeze the dough for at least 2 hours, or until firm.

Preheat oven to 325 degrees F. Line two sheet pans with parchment or Silpat. Arrange the frozen cookies on the pans, 2 inches apart. Bake 12-14 minutes (convection oven) or 16-18 minutes (standard oven), until golden brown. Set the pans on a cooling rack and cool for 5-10 minutes, then transfer the cookies to the rack to completely cool.

First you must make the basic buttercream.

Place the egg whites in the bowl of a stand mixer fitted with the whisk attachment.

Place the 150 grams of sugar in a small saucepan and add the water, stirring until moistened. Bring to a simmer over medium-high heat, stirring occasionally and simmer until the syrup reaches 230 degrees F.

Letting the syrup continue to cook, turn the mixer to medium speed, gradually pour the remaining 33 grams of sugar into the whites, and whip until the whites are beginning to form very loose peaks. If the whites are ready before the syrup reaches 248 degrees F, turn the mixer to the lowest setting just to keep the moving.

When the syrup reaches 248 degrees F, remove the pan from the heat. Turn the mixer to medium-low and slowly add the syrup to the whites, pouring in between the side of the bowl and the whisk. Increase the speed to medium-high and whisk for 15 minutes, or until the bottom of the bowl is at room temperature and the whites hold a stiff peak.

Reduce the speed to medium and add the butter, a few pieces at a time. If at any time the mixture looks "broken" or curdled, increase the speed and beat to re-emulsify it, then reduce the speed and continue adding the butter. If the butter is too loose to hold its shape, it can be refrigerated for up to a few hours to harden, then beaten again to return to its proper consistency.

** The buttercream can be stored in a covered container in the fridge for up to 5 days or frozen up to 1 month. If you make this ahead of time, bring the buttercream to room temperature in the bowl of a stand mixer. Then beat on low to return the buttercream to the proper consistency for piping or spreading.

Combine 175 grams of the basic buttercream with peanut butter and salt and beat for 2 minutes on low, in the bowl of a stand mixer fitted with paddle attachment, until combined and smooth. Transfer the mixture to a piping bag fitted with your choice of tip. Bouchon Bakery recommends Ateco #867 French Star Tip.

Turn half the cookies over. Beginning at the center, pipe a spiral of peanut butter filling, on each one, to within 1/4-inch of the edges. Top each with a second cookie and press gently to sandwich the cookies.

The cookies are best the day they are baked, but they can be stored in a covered container, at room temperature if unfilled, refrigerated if filled, for up to 3 days.