Preheat the Oven: Set your oven to 350°F (177°C) and line your cake pan with parchment paper and lightly grease it.
Mix Dry Ingredients: In a bowl, whisk together flour, baking powder, and salt.
Cream Butter and Sugar: In another bowl, beat the butter and sugar until fluffy and light.
Add Eggs and Vanilla: Beat in eggs, one at a time, followed by the vanilla extract.
Combine Mixtures: Alternately add the dry ingredients and buttermilk to the butter mixture, starting and ending with the dry ingredients.
Pour and Smooth: Transfer the batter into the prepared pan and smooth the top.
Bake: Place in the oven and bake for about 35-40 minutes, or until a toothpick comes out clean.
Prepare Topping: Mix melted butter, sugar, and cinnamon. Brush over the warm cake.
Cool and Serve: Let the cake cool in the pan for 10 minutes, then transfer to a wire rack.