• Preheat to 350 degrees. Line a large cookie sheet with parchment paper. Beat the egg whites with 1/8 teaspoon salt at medium-high speed until stiff peaks form, about 3 minutes. Gradually add in 1 ½ cups powdered sugar, a small amount at a time, and beat until thick and glossy, about 2 minutes. Fold in the almond butter until just blended (the meringue will deflate slightly).
• Using a 1-inch scoop, place 16 mounds of the cookie mixture evenly on prepared cookie sheet. Bake 20 to 25 minutes. Let cool on the sheets for 5 minutes, then transfer to a rack to cool completely.

Make the frosting:

• Using an electric mixer, beat the butter with the remaining 1 ½ cups powdered sugar and ⅛ teaspoon salt on medium speed until fluffy, about 5 minutes. Gently beat in the banana and the lemon juice. Refrigerate 30 minutes before spreading on the cookies.
• Spread the banana frosting on the cooled cookies and sprinkle the chopped pistachios on top.