In a small bowl, combine flour, baking powder, cinnamon, and salt. Set aside.
Using an electric mixer, cream butter and sugar on medium speed until light and fluffy. Beat in egg whites and full egg one at a time, until well combined. Mix in vanilla extract.
On low speed, alternate adding flour mixture with the milk and peach iced tea, beginning and ending with the flour. Mix just until combined.
Evenly distribute batter among the four cake pans. Bake for 26 – 28 minutes.
Honey Mascarpone Frosting
Pour whipping cream into bowl of standing mixer. With the whisk attachment whisk the whipping cream until it becomes fluffy and forms stiff peaks. Transfer whipped cream into a different bowl.
With a paddle attachment on your mixer, beat mascarpone until light and fluffy. Gradually add in honey and beat for 2 - 3 minutes. In the same bowl, gently fold in the whipped cream.
Assembly
With a pastry brush, brush on Peach Iced Tea before layering the brown butter cake layer with frosting. Alternate between cake layer, tea soak, and frosting until you finish off with the final cake layer.
Using a bench scrapper, apply more frosting on the sides of the cake and smooth it out.