Melt the butter and Earl Grey tea in a saucepan over medium heat, stirring occasionally, until it just begins to sizzle. Remove from heat and let cool for 5 minutes.
Add the tea-infused butter, light brown sugar, granulated sugar, salt, and citrus zest to a large mixing bowl. Mix on medium speed for about 30 seconds until grainy and separated.
Add the egg and vanilla extract and mix for another 30 seconds until combined and smooth.
In a separate bowl, whisk together the flour, baking powder, and baking soda. Add the dry ingredients to the wet ingredients and mix with a rubber spatula until just combined.
Roll 2-tablespoon portions of dough into balls and coat them in granulated sugar. Place the balls on a parchment-lined baking sheet, spacing them about 2 inches apart.
Bake at 350°F for 16-19 minutes, rotating the baking sheets halfway through if using two sheets. Remove from the oven and let cool on the baking sheets.
