In a medium pot, heat the milk, cream, and lemon rind on medium/low heat, until very hot but do not boil. Remove from heat and let cool to warm.

In a medium pot add the yolks and sugar, whisk together until combined, then add the flour and vanilla, whisk again until smooth.

Place the pot back on the stove on medium/low heat, and pour the warm milk/cream mixture through a sieve to remove the lemon rind (discard). Whisk continuously until thick.

Remove from the heat and let cool for about 15 minutes. Then move to a glass bowl, cover with plastic wrap (make sure the plastic is touching the cream) and refrigerate for approximately 1-2 hours.

While the pastry cream is in the fridge, make the cookie dough. In a mixing bowl or food processor whisk together the flour, baking soda, sugar, salt and zest, then add the yolks and butter. Pulse or mix with the flat beaters to form a compact dough.

Move the dough to a flat surface and form into a dough ball. Wrap it in plastic and refrigerate for approximately 45-60 minutes.

Pre-heat oven to 350F (180C). Line a large cookie sheet with parchment paper.

Remove the dough and pastry cream from the fridge. Roll the dough on a lightly floured flat surface to a ⅛" thickness, make 20 cut outs with a medium round cookie cutter (about 3 inches/7cm).

Give the pastry cream a stir, then place a heaping teaspoonful of it in the middle of 10 of the dough circles and cover each one with another round, gently making a slight dome.

Seal the edges with wet fingers, if you prefer you can seal it first with the tongs of a fork, then again with wet fingers. Place on the prepared cookie sheet.

Bake for approximately 12-14 minutes. Let cool on the cookie sheet, then move to a wire rack, when cool dust with powdered sugar or drizzle with the lemon glaze. Enjoy!

In a small bowl mix together the powdered sugar, cream and lemon juice. Add more powdered sugar or lemon juice depending on desired thickness.