1. Combine the flour and 1 cup of the cashews in a food processor and process together into fine crumbs. Set aside.
2. Make sure the bowls, beaters, and utensils used are very clean and free of yolk or fat particle which can interfere with proper whipping. Yolks and whites are easy to separate when the eggs are cold but bring the egg whites to room temperature for 30 minutes before beating to ensure volume.
3.In a bowl of a stand mixer, beat egg whites on medium-high speed until frothy. Sprinkle in cream of tartar and continue to beat until soft peaks form.
4.With the mixer running continuously, gradually add the sugar. Continue to beat until the egg whites form stiff peaks. To test, tip the bowl, and if the meringue doesn’t slide off, it’s ready.
5. Add the vanilla extract and about 1/3 of the flour/cashew mixture. Gently fold them into the meringue using a rubber spatula, making sure not to deflate the whipped egg whites. Fold the rest of the flour/cashew mixture in two more additions.
6.Transfer the meringue in a large piping bag fitted with a large piping tip.
7.Pipe the meringue on the prepared baking sheet at about 1/2 inch in height.
8.Using a knife or an offset spatula, flatten and smoothen the tops of the meringue circles. Gently tap the baking sheet on the counter to remove any bubbles.
9.Bake in a 325 F for 17-20 minutes or until lightly browned.
10. Using a spatula, transfer the cookie wafers to a cooling rack. The edges will be crisp and the middles soft.
Allow to completely cool while making the buttercream.
1.In a medium saucepan, stir together the sugar and water. Let the mixture boil over medium heat. Once boiling, place a candy thermometer in the pan to monitor the temperature. It should reach 238 F before adding it in a thin stream to the beaten egg yolks.
2.Meanwhile, start to beat the egg yolks on a stand mixer on high speed until they start to thicken and become pale in color.
3.Continue to beat while the sugar/ water mixture cooks in the pan. Once the temperature of the mixture reaches 238 F, turn the heat off and slowly pour the sugar syrup in a thin, continuous stream into the yolks with the mixer still running.
4.Continue beating the yolks until the mixing bowl is cool to the touch.
5.With the mixer still running, add the softened butter, about a tablespoon at a time. Beat until a fluffy buttercream forms. Make sure to take the butter out of the fridge about 2-3 hours ahead to bring to room temperature. It should be soft but not melting or it will make the buttercream grainy.
6. If you like to add flavor, add a few drops of extracts such as ube, langka or pandan to the buttercream and refrigerate for a few minutes. Whip it again for easier spreading.
7. Spread the buttercream minimally. The amount of buttercream in the recipe is enough to fill and coat 13 cookie sandwiches.