Preheat oven to 375°F. Coat a nonstick mini muffin pan with nonstick spray, set aside.
In a large bowl mix together coconut, sugar, flour, vanilla, and egg whites until evenly combined.
Spoon 1 tablespoon of coconut mixture into each liner or cup. Press coconut mixture into bottom and up sides to form a thin crust.
Bake for 12-13 minutes or until edges are lightly browned, watching carefully not to burn. Transfer pan to a wire rack.
Reduce oven temp to 350°F.
In a medium bowl stir together yolk, sweetened condensed milk, and lemon juice until smooth. Spoon filling into warm crusts, enough to fill cup, but not overflow. You will have a little leftover filling.
Bake for 10 minutes. Allow tassies to cool in pan for 10 minutes before transferring to a wire rack to cool completely. If you did not use a liner, run a butter knife around sides to loosen from pan.
Store airtight in refrigerator for up to 7 days.
