Preheat your oven to 350°F (180°C) and line a 12-cup cupcake pan with liners.
In an electric mixer fitted with the paddle attachment, cream the unsalted butter and sugar together on medium speed until fluffy (2-3 minutes).
Add the egg, followed by the egg white, and then the Earl Grey milk mixture, beating until smooth between each addition.
In a separate bowl, whisk the flour, baking powder, baking soda, and salt together. Then cut open the third Earl Grey tea bag and whisk in ½ tsp of the tea leaves into the flour as well.
Add the flour mixture to your wet ingredients and fold on low speed until the flour is just combined.
Take ¼ cup of your roasted blackberries and use a flexible spatula to gently swirl them into the batter.
Divide the batter evenly between the 12 lined cupcake tins. Bake for 19-21 minutes, or until cupcakes are set and a toothpick comes out clean. Let the cupcakes cool for 10 minutes in the pan before transferring them to wire racks to cool completely.