Preheat your oven to 350°F (175°C) to ensure even baking.
Grease and flour a 9x13 inch baking pan to prevent sticking.
In a large mixing bowl, whisk together the flour, salt, baking powder, and baking soda. Set aside.
In another bowl, use an electric mixer to cream the softened butter and 2 cups sugar until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition to incorporate air for a lighter texture.
Gradually add the dry ingredient mixture to the butter mixture, alternating with the buttermilk. Begin and end with the flour mixture. Mix until just combined; do not overmix.
Pour the batter into the prepared pan and spread evenly. Bake for 40-45 minutes until a toothpick inserted comes out clean.
While baking, prepare the glaze by combining 1/3 cup butter, 3/4 cup sugar, 2 teaspoons vanilla, and 3 tablespoons water in a saucepan over medium heat. Stir until sugar dissolves and mixture is smooth.
Remove cake from oven and cool for 10 minutes in the pan. Poke holes all over the top with a fork or toothpick, then pour the warm glaze evenly over the cake to soak in.
Allow the cake to cool completely in the pan before cutting into squares and serving.