Preheat oven to 300F. Line a cookie sheet with parchment paper, lightly grease and set aside. To end up with cookies that’s the same shape and size, you can create a guide by tracing a cookie cutter (or anything round) at the back of your parchment paper then flipping that over. You want your cookies 2-3 inches in diameter.
Using a stand mixer fitted with the whisk attachment or a handheld electric mixer, whisk 5 egg whites on medium-high speed until foamy.
Add ½ tsp cream of tartar and continue whisking until you reach soft peaks.
Gradually add ½ cup sugar until you reach stiff peaks.
Remove the bowl from the mixer and gently fold your ground cashews into the meringue, careful not to deflate it.
Transfer the meringue into a piping bag (or a large Ziploc bag with one corner cut off) and pipe onto your prepared baking sheet. Smoothen the tops with an offset spatula.
Bake for 20 minutes or until the sides turn a light brown. Turn the oven off but leave the cookies in the oven for another 10 minutes.
Take out of the oven and allow to cool before removing from the baking sheet (see notes).
For the French buttercream filling:
While your cookies are baking, you can work on your buttercream. Start by boiling water in a large pot, then bringing it to a simmer (see notes).
In a large stainless steel bowl (I like using the bowl of my stand mixer), whisk 5 egg yolks, ⅓ cup + 1 tsp granulated sugar, 2 tsp vanilla extract and a pinch of salt.
Place bowl over simmering water and constantly stir/scrape the sides so the egg yolks don’t scramble. You need this mixture to reach 155F/68C to make sure the yolks are cooked through (see notes).
When it’s ready, transfer the bowl to your stand mixer fitted with the whisk attachment and whisk at high speed until it’s light, fluffy and stiff (6-8 minutes). If you touch the bottom of your bowl it should not be hot anymore.
With the mixer still on, start adding your butter and continue whisking until your buttercream is thick and creamy.
If you’re not using the buttercream right away, transfer to an airtight container and refrigerate. You may need to re-whip before using.
For the assembly:
Now you’re ready to assemble! Combine the graham crackers with the ground cashews.
Take a fully cooled cookie, spread some buttercream on the uneven side and sandwich with another cookie (again, smooth side out).
Fill in the sides and smoothen it out.
Roll the cookie in graham cracker cashew crumbs. Proceed to frost and coat the rest of the cookie (see notes). Freeze to allow the cookie to set. Best served cold.
Video
Notes
Don’t remove the cookies too early from the cookie sheet, they will stick and break. Don’t leave on the sheet too long either, they will become too brittle. You know they’re ready if they detach from the sheet easily and in one piece (you may need a sacrificial cookie for testing!).
You don’t need too much water; depending on how big your pot is, 1.5 to 2 inches of water is fine. Just make sure your pot is wide enough so your mixing bowl will fit in but not too wide that the bottom of your bowl will touch the bottom/hot water.
A thermometer is absolutely necessary here, you can get one for less than $15.
Check out the post for tips on how I frost and assemble my silvanas.