• Preheat the oven to 350 degrees fahrenheit. Spray a 9-inch cake pan (with 2-inch high sides) with pan spray and line with a round of parchment paper for easy removal.
• In a large bowl, combine the butter, brown sugar, granulated sugar, egg, and vanilla until combined. Mix in the buttermilk.
• In a small bowl, whisk together the flour, baking soda, and salt. Add to the wet ingredients and mix until just combined.
• Add the cake batter to the prepared pan and bake for 30-35 minutes, until a toothpick comes out clean from the center of the cake.
• Let the cake cool for 15 minutes before poking all over with a skewer and pouring the glaze evenly over the top. You can place a pan or parchment paper under the cooling rack to catch the excess glaze as it spills over the sides of the cake.

Glaze

• Once the cake has been removed from the oven and is cooling, begin making the glaze. Add the butter to a small saucepan and cook over medium heat until fully melted.
• Reduce the heat to low and add the brown sugar, vanilla, and buttermilk. Stir until the sugar is completely melted. Remove from the heat and stir in the powdered sugar and salt.