These cookies are delicately infused with the floral flavours of Earl Grey tea with a touch of citrus. If you don't have loose-leaf tea simply use two tea bags.
Heat oven to 350 F and line two sheet pans with parchment paper.
Combine the butter and Earl grey tea leaves in a small saucepan set over low heat: cook until it is melted and comes to a simmer. Remove from the heat, strain the tea leaves from the butter with a small sieve and set aside.
In a large bowl, add the melted butter, sugar, brown sugar, and orange zest. Use an electric mixer on medium speed or a whisk to combine. Add the eggs, one at a time, along with the vanilla, and mix until combined and smooth, about 30 seconds.
Add the flour, baking powder, baking soda and salt to the bowl, and mix on low speed or with a rubber spatula until combined.
Roll about 2 tablespoons of dough in a ball, place on the baking sheets 2 inches apart, and gently press with the palm of your hand to slightly flatten.
Bake the cookies until they are a light golden brown around the edges, around 12 minutes. Transfer the cookies to a cooling rack and drizzle with icing, if desired. Store extra cookies in an airtight container at room temperature for up to 3 days, or up to 1 month in the freezer.
Whisk together the icing sugar and milk until smooth. Drizzle over the cooled cookies and grate a bit of orange zest on top if desired.