Heat oven to 500 degrees, and position your baking rack in the top third of your oven.
Mix flours, sugar, poppy seeds, baking powder, baking soda, lemon zest, and salt in a bowl with a whisk.
Add grated or cut butter to mixture and cut in with a pastry cutter. I choose to simply use my microplane that I had already used for the lemon zest to grate my butter.
Whisk together egg and lemon juice and add to the flour mixture, mixing with a wooden spoon.
Add heavy cream to mixture and use wooden spoon to combine as best you can. You'll probably need to get your hands in there to work it all together, but be careful not to overwork the dough.
Divide the dough into two balls and flatten each half into a 6-inch disk. Cut each round into 6 equal pieces.
Transfer scones to a baking sheet and sprinkle with granulated sugar if desired. Adjust oven temperature down to 450 degrees and bake the scones until they're golden brown, about 14 minutes.
For the glaze:
Whisk together 2 tablespoons of fresh lemon juice and ½ cup confectioners sugar until smooth.