Preheat oven to 375 degrees.

In a small bowl, mix together the egg yolk, cold water, and vanilla.

Using a stand mixer with a flat beater attachment, mix the flour, almond flour, sugar, salt, and baking powder.

While mixing, add in the very cold butter cubes.  Continue mixing until you achieve a consistency like cornmeal.

Add in the egg mixture and beat until smooth.

Gather the dough into a ball, cover with plastic wrap and chill for 30 minutes.

Roll out the dough making a thin sheet and place in the tart pan.  Using a fork, poke some holes in the bottom.

Bake at 375 degrees for about 12 minutes until the crust begins to brown.

Allow to cool and set aside to add the filling.

Heat a pot of water to 149 degrees.

Place the egg yolks in a zip top bag expelling as much air as possible.

Cook the yolks for 35 minutes, maintaining a water temp of 149 degrees.

While the eggs are cooking, combine the sugar and lemon juice in a medium saucepan.

Boil until the sugar dissolves completely (about 2-3 minutes).

All the syrup to cool to room temperature.

When the eggs have finished cooking, immediately submerge the bag into ice water.

Pour the cooked egg yolks into a blender (cutting a corner of the bag and emptying it like an icing back makes this easier).

Gradually add the sugar and lemon syrup while blending.

Add the cubes of butter gradually and blend until homogenous.

Add the lemon zest and perform a final blend.

Pour the mixture into your tart crusts and chill in the refrigerator for at least 4 hours.  The liquid mixture will thicken to become firm.

Serve cold with dollop of whipped cream.