Steep the 2 tbsp. tea in 1 c. hot water for 10 min.

Preheat oven to 325°F. Generously butter and flour a loaf pan. Chill 10 min.

Whisk together flour, baking powder, and salt.

Stir together milk and vanilla in a small bowl.

Beat together butter and 1/2 c. plus 2 tbsp. sugar in a large bowl with an electric mixer until fluffy. Add eggs 1 at a time, beating well after each addition.

Alternately add flour and milk mixtures to butter and eggs in 4 batches, beginning with flour and mixing at low speed until each batch is just incorporated. Mix in remaining sugar until just combined, then tea.

Spoon batter into pan, smoothing top, and bake in middle of oven until golden brown on top and a toothpick inserted into center comes out clean, about 1 hour. Carefully loosen edges with a knife and immediately invert cake onto a rack to cool completely.

Icing:

Gradually add confectioners sugar to 1 tbsp. rooibos tea, whisking until smooth and adding more tea, 1 drop at a time, if glaze is too thick. Drizzle decoratively over top of cake.