Preheat oven to 400°F (200°C). Line a half sheet baking pan with parchment paper and set aside.
In a large mixing bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt for about 20 seconds to evenly distribute leaveners.
Add cold butter cubes to dry ingredients. Use a pastry cutter to work butter into flour until mixture resembles coarse crumbs with pea-sized butter pieces still visible.
Reserve 1 tablespoon of lavender for topping. Add remaining 1 tablespoon lavender and lemon zest to flour mixture, tossing gently with a fork to distribute evenly.
In a small bowl, whisk together heavy cream, egg, and vanilla extract until smooth.
Pour wet ingredients into dry mixture and stir gently with a spatula just until a shaggy dough forms. Stop as soon as no dry flour remains visible.
Turn dough onto a lightly floured surface. Pat gently into an 8-inch wide, 1-inch thick circle without using a rolling pin. Cut into 8 even wedges with a bench scraper or sharp knife.
Transfer wedges to prepared baking sheet, spacing 2 inches apart. Freeze for 10 minutes before baking.
Brush tops with extra heavy cream, then sprinkle with reserved lavender buds and turbinado sugar. Bake for 15-18 minutes until golden brown. Cool on pan for 5 minutes, then transfer to wire rack.
While scones cool, whisk together powdered sugar, honey, and 2 tablespoons milk in a small bowl. Add remaining milk a teaspoon at a time until glaze is smooth and drizzles easily.
Once scones have cooled for about 10 minutes, drizzle glaze generously over tops. Let glaze set for a few minutes before serving.