Preheat oven to 400 F., line a baking sheet with parchment paper, and chop 1 cold stick (4 oz.) of butter into smaller pieces so it can warm slightly while you prepare your other ingredients.
In a large mixing bowl, combine 2½ cups flour, 1 tsp. baking powder, 1 tsp. baking soda, ½ tsp. kosher (or flake) salt, ⅓ cup sugar, 1 tsp. poppy seeds and zest from 1 lemon. Mix gently. Set aside.
In a separate small mixing bowl, combine 1 beaten egg, ⅓ cup lemon juice, ¼ cup heavy cream and 1 tsp. real vanilla extract. Set aside. (You'll add these ingredients to your dough after you've mixed in the butter.)
Add your semi-softened butter to the large mixing bowl. Use your hands to mix it into the flour until you have a crumbly mixture, allowing a few bits of butter to stay unmixed. This allows nice pockets of butter to form in your scones.
Add the contents of your small mixing bowl to the large one, and mix with a spoon until thoroughly combined into a sticky dough. Get your hands nice and floury to make it easier to pick up and roll dough with your hands.
Pick up about 2 tbsp. of dough with your hands and roll it into a ball. Flatten it and add 2 frozen raspberries. Fold and roll it back up into a ball. Place it on parchment-lined baking sheet and repeat with the rest of the dough. Bake scones for 15-20 minutes on the bottom rack.
While your scones bake, make your glaze. In a small mixing bowl, combine ½ cup confectioners sugar, ½ tsp. lemon zest and 2 tbsp. fresh lemon juice.
After 15-20 minutes, remove your scones and allow them to cool for 5 minutes. Then, use a pastry brush to coat them in the lemon glaze. Refrigerate them for about 5-10 minutes to help the glaze set, then serve.