Prep your oven and pans: Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
Mix the dry ingredients: In a medium bowl, whisk together flour, Earl Grey tea, lavender, baking powder, baking soda, and salt.
Cream the sugar and butter: In a stand mixer with the paddle attachment, beat sugar and butter on medium-high speed until light and fluffy, about 2-3 minutes. Scrape down the sides as needed.
Add the egg and vanilla: Reduce the mixer speed to low and add the egg. Pour in the vanilla extract and beat until just combined. Scrape down the bowl again.
Add dry ingredients: With the mixer on low, slowly add the dry ingredients and mix until just combined. Scrape down the bowl once more and mix on low for an additional 30 seconds.
Assemble the cookies: Use a 3-tablespoon cookie dough scoop to form dough balls. Place them on the prepared pans, leaving 3 inches between each. Sprinkle the tops with the remaining 2 tablespoons of sugar.
Bake the cookies: Bake one tray at a time for 12 minutes. The cookies should be set at the edges but still gooey in the center. They’ll puff up during baking but will flatten and crack as they cool.
Garnish and cool: If using, sprinkle blue cornflower petals over the cookies while they cool. Let the cookies cool on the baking sheet for about 20 minutes until firm.
Serve and store: Enjoy warm or at room temperature. Store leftover cookies in an airtight container at room temperature for up to 3 days.