Combine almond flour and powdered sugar in a food processor and process until very fine, about 40 seconds. Sift into a bowl to remove any large clumps.
In a stand mixer, whip eggs on medium-high speed until soft peaks form. Add granulated sugar and cream of tartar while machine is running. Continue to whip until stiff and glossy peaks form.
Using a rubber spatula, gently fold in almond flour mix one third at a time. Do not over mix. Transfer mixture into a large piping bag.
Pipe 1-inch circles onto the parchment paper, leaving 2-inches of space in between. Tap trays against the countertop to release extra air from cookies. Let sit for 30 minutes, until they form a dry skin.
Bake 18 to 20 minutes, turning pans halfway through baking. Keep a close eye, as they will brown quickly.
Let cookies cool completely before removing from pans.
For filling, beat butter with salt until fluffy, about 2 minutes. Slowly add powdered sugar and vanilla and beat until light and smooth, about 3 to 4 minutes. Transfer to piping bag and pipe between two cookies.