Preheat your oven to 350°F (175°C). Line your cupcake tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, salt, chai spice blend, and espresso powder until well combined.
In another bowl, combine the melted butter, eggs, and milk. Whisk until smooth and fully combined.
Gradually pour the wet ingredients into the dry ingredient mixture. Stir gently until just combined; avoid overmixing!
Spoon the batter into cupcake liners, filling each about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.
In a saucepan, melt the butter over medium heat, stirring frequently until it turns golden brown and has a nutty aroma. Let it cool before mixing with powdered sugar and milk until smooth and fluffy.
Once the cupcakes are completely cool, frost them generously with the brown butter frosting!