In a medium size bowl, cream together shortening and sugar.
Add eggs, milk, and vanilla. In a separate bowl, mix dry ingredients (flour, baking powder, and salt).
Slowly mix dry ingredients into the wet mixture until you form a large dough ball.
Refrigerate for at least 30 minutes or overnight.
When ready to bake, preheat oven to 350 degrees F and grease well a standard size muffin tin.
Roll dough into 1'' balls and pat gently in your hand to flatten.
Place into your muffin tin and press it down flat and up along the sides of the muffin tin. You want it to be pretty thin (at least 1/4''in thin).
Repeat with remaining dough. Bake for 8-10 minutes. (If you've found that they didn't keep their indented shape, remove them from the oven at 8 minutes and use a small spoon to press them back down along the sides of the muffin tin. Then bake them for an additional 3 minutes.).
Remove from oven and allow to cool for a few minutes.
Then use a knife to trace along the outside of the cups to loosen them. Remove them onto a wire cooling wrack to cool completely.
For the Creamy Lemon Filling:
Crack eggs in a small bowl, beat slightly with a fork and set aside.
In a large saucepan combine sugar and cornstarch.
Whisk in milk and fresh lemon juice.
Cook over medium heat, stirring constantly, until mixture is thick and bubbling.
Reduce heat to low and cook for two more minutes.
Add a spoonful of the hot mixture into the egg yolks and stir well. Repeat this process with two or three more spoonfuls of the hot mixture added to the egg yolks. (The goal is to temper the egg yolks so they don’t cook when added to the hot saucepan.)
Poor egg mixture into the saucepan and stir well.
Bring mixture to a gentle boil and cook for two more minutes. Remove from heat.
Add softened butter and lemon zest and stir until butter melts completely.
Allow mixture to cool and then stir in Greek yogurt.
Spoon a heaping tablespoon filling into each cookie cup.
Refrigerate for at least 30 minutes before topping with fresh fruit.