Instructions

Make the Dough

1. Combine the butter, sugar and salt in a mixer bowl and mix until softened and combined, do not aerate. Add the flour and mix just until a dough is formed. Split the dough into 2 equal portions
2. (At this stage the dough can be wrapped and refrigerated or frozen for later use).

Assemble the shortbread

1. Preheat the Oven to 350°F. Place a 1/2 sheet of parchment paper off to the side on the work surface. On another area of the work surface roll one disc of dough into a 12" round (1/8" thick). Transfer to the rolled dough to the parchment sheet.
2. Spread the curd over the the dough round, leaving a 1/2" border around the edge. Brush the border with egg wash.
3. Roll the other dough to a 12" round. Roll the 2nd dough round onto the rolling pin and unroll onto the curd covered bottom layer. Use a paring knife or pizza cutter to trim the ragged edges of the shortbread round.
4. Use a fork to crimp and glue together the edges. Prick the shortbread all over with the fork to create steam vents. (At this stage the round can frozen for later use).
5. Use a long serrated knife to lightly score the shortbread into 12 wedges, being careful not to cut through the top layer. Sprinkle the shortbread round with 1 tablespoon granulated sugar.
6. Bake until the dough is lightly golden and baked through, about 20 minutes.
7. Allow to cool to room temperature and cut along score lines.

Instructions

1. If you are using the gelatin, bloom in 2 tablespoons cold water in a medium size bowl. Set aside.
2. Thoroughly whisk together the sugar and eggs in a medium saucepan. Add the lemon juice, zest and salt.
3. Place the butter on top of the bloomed gelatin. Put a fine mesh sieve over the bowl and keep it near the stove.
4. Heat the egg/juice mixture over medium low heat, stirring constantly. You must be sure to keep stirring across the entire bottom and corners of the pot so the custard does not have a chance to stick. The mixture will start out opaque with a fine white foam over the surface. As it heats up the curd will thicken, become more translucent and the foam will disappear.
5. Cook until the curd will coat the back of a wooden spoon and just begins to boil. Don't allow it to come to a rolling boil. One or two bubbles is all you need to see.
6. Immediately remove from the heat and pour through the sieve over the butter and gelatin. You can skip straining the curd if you like the bits of zest in the curd.
7. Stir until the butter and gelatin are melted and thoroughly incorporated. Cover the bowl with plastic wrap and cool a bit before putting in the refrigerator.
8. Refrigerate until completely cooled. If using gelatin, allow it to sit 8 hours or overnight to gel.