Preheat the oven to 350°F. Spray a 9″ round cake pan with baking spray and line with parchment paper. Set aside.

Combine the butter and brown sugar and stir until smooth. Add the egg, beating again till smooth. Stir in the buttermilk and vanilla extract. Sprinkle the flour, baking soda and salt evenly over the top and still until well combined. Pour the batter into the prepared pan.

Bake the cake for 30 minutes or until a toothpick inserted in the center comes out clean and/or the cake springs back when lightly touched in the center.

During the last 10 minutes of baking time, prepare the topping. Stir the butter and the sugar together. Add the milk, pecans, and salt. The glaze will be thick, but pourable.

After the cake has baked for 30 minutes, pour the topping over the cake and return it to the oven for another 10 minutes (for a total baking time of 40 minutes). Remove cake from the oven and allow to cool for 20 minutes in the pan.

Sprinkle lightly with flaky sea salt, if desired and serve warm or at room temperature. Topping will firm up as the cake cools. Cake can be served in the pan or on a serving platter or cake stand. To serve on a platter, invert cake onto a dinner-size plate then invert again so that topping is up.