Preheat oven to 350 degrees. Grease 9 cups of a muffin tin. Cut 1/2-inch wide strips of parchment paper and place into the cups of the muffin tin, allowing the ends to hang out on both sides. This will create a little "sling" that will make removing the tarts easier later.

Place the cookies in a food processor and pulse until finely ground. Place the cookies in a bowl and mix with the brown sugar. Add the melted butter and stir to thoroughly combine (the mixture will still be crumbly - don't worry, there is enough butter in the cookies to hold the mixture together once baked).

Place about 1 heaping tablespoon of the crust mixture into each of the muffin cups, pressing the mixture down into the bottom of the cup. (Using the bottom of something like a spice jar to tamp down the crumb mixture might make this easier.)

Bake for 6-8 minutes, until the edges are golden.

While the crust bakes, make the filling.

In a medium bowl (or a large liquid measuring cup - this will make for easy pouring later), whisk together the eggs and sugar until light yellow. Add the lemon juice, zest, and flour and whisk thoroughly to combine.

Once the crust comes out of the oven, pour the filling on top of the hot crust, equally distributing over each of the cups. Return to the oven and bake for another 9-11 minutes, until the centers are set.

Allow to cool in the tin. To remove, run a paring knife around the edges, then use the "slings" to lift them out of the tin. Remove the parchment sling.

Just before serving, dust the tops with powdered sugar.

Store in an airtight container in the refrigerator for up to 4 days.