In a large bowl, whisk together salt and flour. Break butter into small chunks and add them in. With your fingers, loosely rub the butter into the flour mixture until butter is in small bits and pieces.

Make a well in the center of the mixture pour about 2/3 of the cold water. Mix everything until mixture has come together into a firm, rough dough. If the mixture is still crumbly and falling apart, you can add a little water at a time as needed. Cover the bowl with plastic wrap and chill in the fridge for at least 20 minutes.

Turn mixture into a lightly floured board. Form a rectangle by gently kneading and patting the dough. Using a rolling pin, roll the dough to about 8 x 18 inches in size. Roll in one direction only and don't overwork the butter. The rolled dough should look like a marble because of the butter streaks. Keep the edges straight.

Fold the upper third of the dough down the center, then fold the lower third over it ( like folding a business letter). Turn the dough so that the shorter edge is facing you. Roll the dough again to about 8 by 18 inches in size. Fold again like a business letter and chill in the fridge for at least 20 minutes.

In a sauce pan over low heat, melt cream cheese with milk and cream. Once cream cheese is melted ( a few small lumps of cream cheese is okay) , turn off heat and add the egg whites, sugar and vanilla extract. Stir everything gently with a fork or whisk until the egg whites are incorporated into the mixture. Transfer filling into a container with spout and keep chilled in the fridge while you prepare the crust. This filling mixture can be made ahead for 24 hours before using.

Without unfolding the dough, cut it in half. Leave the other half in the fridge while you work on the other. On a floured board, roll dough to about 1/8 inch thickness. Using a circle cutter of about 5 inches in diameter, cut circles from the dough. (You can use the rim of coffee mugs or lid of pint containers.)You can make about 7 circles from each half. Gather the scraps, stack them together and wrap in plastic to chill in the fridge.

Place the oven rack in the lowest position and preheat oven to 400 F. Fit each circle of dough into the holes of a regular muffin pan, leaving one hole of space in between most of them. There should be about 1/8 to 1/4 inch overhang of dough on the edges. Lay a piece of parchment paper on each crust, fill with uncooked rice or beans.

Bake the crusts in the lowest rack of oven for 17- 20 minutes. Remove pan from oven, take off the parchment paper with the rice and prick the surface of the crusts all over with a fork. Bake the crusts for 5-7 more minutes or until the crust is lightly browned. Turn off oven but leave the crusts inside with the door open for 5 more minutes. Take out pan and dial oven temperature to 325 F. Brush the surface of the crusts with egg whites and bake in the oven for an additional 5 minutes. Let crusts cool completely.

Note: at this point, you can repeat the entire assembly and pre-baking procedure with the other half of the puff pastry dough( including the scraps), so that all crust are pre-baked prior to baking the filling. Or you can go ahead and bake the filling and save the rest of the puff pastry dough and filling to bake for the next day.

Position the rack in the middle of the oven. Preheat to 325 F. Once the oven has reached the desired temperature, quickly stir the filling and gently pour into each of the cooled crust up to 2/3 full. Bake for 25-28 minutes or until the edges of the filling look set and the middle is slightly jiggly.

The scraps, when stacked together and rolled, can still make up to 6 circles of dough for an additional 6 egg tarts. The filling should be just about enough for the entire puff pastry dough 18-20 tarts.)