Preheat the oven to 350℉. Grease a 9x13 cake pan with butter and set aside.
In a large bowl, whisk together flour, baking powder and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter and sugar on medium-high speed until light and fluffy, about 3 minutes. Add eggs and egg yolk, one at a time, beating well after each addition. Mix in the vanilla. Scrape down the sides and bottom of the bowl as necessary.
Add half the flour mixture and beat just until combined. Mix in the sour cream. Add remaining flour mixture and mix just until combined.
In a separate bowl, whisk together the brown sugar and cinnamon.
To assemble, transfer half the cake batter to the cake pan. Spread into an even layer. Sprinkle half the cinnamon sugar mixture evenly over the batter. Repeat with remaining cake batter (it helps to drop in dollops). Spread into an even layer, then sprinkle remaining brown sugar cinnamon mixture on top. Use a knife to swirl with a knife.
Bake cake at 350℉ for 30 to 35 minutes or until a toothpick inserted in the center of the cake comes out with just a few crumbs.
For the glaze, whisk together confectioners’ sugar, milk, honey and vanilla. Pour over the warm cake. Cool completely and allow glaze to harden before slicing and serving.
Notes
Sour cream may be substituted by full-fat Greek yogurt.Store covered at room temperature for 3 days or refrigerated for 5 days.