In a small saucepan, combine butter and tea leaves over medium heat. Once butter melts and begins to boil, reduce heat to low, and cook for 5 minutes, stirring occasionally. Remove from heat, cover, and let steep for 20 minutes.
Strain butter through a fine-mesh sieve, discarding any solids. Refrigerate butter until firm, but still soft and spreadable, approximately 20 minutes.
In the heatproof bowl of a stand mixer, whisk together egg whites, sugar, and honey. Place bowl over a saucepan of simmering water. Cook, whisking frequently, until an instant-read thermometer registers 160°, approximately 2 minutes.
Carefully return bowl to stand mixer. Using whisk attachment, beat at high speed until meringue has thickened and cooled to room temperature, 3 to 5 minutes. Add butter, 1 tablespoon at a time, beating until combined after each addition. Beat in salt. Beat until buttercream comes together and thickens. (Buttercream may look curdled at first, but keep mixing and it will soon emulsify. This can take up to 10 minutes.) Use immediately, or transfer to an airtight container and refrigerate for up to 1 week. When ready to use, let come to room temperature, and beat with a stand mixer fitted with the whisk attachment at high speed until fluffy.
Notes
*We used Evergreen Oolong from Mark T. Wendell Tea Company, available at marktwendell.com or 978-635-9200. If this oolong is not available, any lightly oxidized semi-balled oolong with floral notes can be substituted.
Recipe by TeaTime Magazine at https://teatimemagazine.com/oolong-chocolate-cakes/