In a bowl, whisk together heavy cream, egg, vanilla, and lemon zest. Set aside.
In a large bowl, whisk together the flour, sugar, poppy seeds, baking powder, and salt.
Using a box or hand grater, grate the frozen butter into the flour mixture. Using floured hands, toss the butter with the flour breaking up any large pieces of butter.
Pour the wet ingredients over the flour and butter mixture. Using a fork or spatula, mix until a dough forms.
Dump the dough onto the counter and gently work with floured hands until the dough comes together in a ball. Avoid overworking the dough.
Transfer the dough ball to a sheet of parchment paper. Using your hands, press it into a round disk about 3/4 inch thick.
Using a sharp knife, cut the dough into 8 equal triangles.
Transfer the dough and the parchment to a plate. Brush the top with heavy cream and chill in the fridge for at least 30 minutes.
Meanwhile, preheat the oven to 400 degrees F and line a large baking sheet with parchment paper.
Transfer the chilled scone dough to the parchment-lined baking sheet leaving 2 to 3 inches between each triangle.
Bake for 18 to 20 minutes or until the edges and tops are lightly browned. Allow the scones to cool for 10 minutes.
Meanwhile, make the glaze by whisking together the powdered sugar, lemon juice, and heavy cream until well combined and smooth.
Using a fork, drizzle the glaze over the scones. Enjoy!
Notes
It's important to keep the butter as cold as possible. If at any point the butter starts to soften, transfer everything to the fridge to chill for 10 minutes before moving on.
Store the scones in an airtight container at room temperature for 2 to 3 days or in the fridge for up to 1 week. Note, chilling the scones will cause them to dry out a bit.