Combine 4 tablespoons of the butter, sugar, lemon juice, and lemon zest, sugar in a medium saucepan and bring to a boil. Meanwhile, whisk the egg yolks together in a medium bowl. When the lemon juice liquid comes to a boil, remove from heat and slowly add to the eggs in a small steady stream while whisking continuously.

Return the mixture to the saucepan and continue to cook on medium heat, whisking constantly, until thickened, about 5-7 minutes. Remove from heat and strain the curd through a mesh strainer into a medium bowl. Stir remaining 2 tablespoons of butter into the curd. Chill in the fridge for at least 2 hours or overnight.

To make the biscuits, preheat the oven to 400 degrees F and line a sheet pan with parchment paper.

In a large bowl, stir together the flour, sugar, baking powder, salt and lemon zest. Add the butter and use a fork or a pastry blender to cut the butter into the dry ingredients. Add the cream and stir until just combined. Turn out onto a flour surface and lightly knead the dough to incorporate all crumbly bits of dough.  Do not overmix.

Press dough out to about 2 inches thick and cut into 2-3 inch rounds. Place on the prepared sheet pan, leaving 1 inch between each biscuit. Brush tops with whipping cream. Bake until tops are golden brown, about 20 minutes. Let cool completely.

Whip the heavy whipping cream to soft peaks. Add the sugar and vanilla an whip to medium peaks.

To serve, slice the shortcakes in half. Spoon lemon curd on the bottom half of the shortcakes, followed by whipped cream and berries. Top with top half of the shortcakes.