Combine the flour, baking soda (bicarbonate of soda) baking powder,½ and salt in a bowl.
Using a stand mixer or handheld beater, beat the butter and sugar for about 3 to 5 minutes on medium-high speed until light and fluffy. SEE NOTE 3
Add eggs, one at a time, beating after each addition. Beat in the vanilla extract.
Add the flour mixture to the beaten butter and egg mixture.
Beat for about 15 seconds then add in the buttermilk. Beat until just combined. Do not overbeat.
Pour the mixture into a greased and lined square 9 inch (23cm) pan
Bake in a preheated oven of 320°F (160°C) for 30 to 35 minutes until a toothpick inserted into the center comes out clean. SEE NOTE 4
Remove the cake from the oven and let it cool in the tin for about 8 to 10 minutes before turning out onto a wire cooling rack.
To make the butter sauce
Combine the water, sugar, butter, and vanilla extract in a pot.
Cook on medium heat just until the butter is melted and the sugar has dissolved.
You can either use the sauce immediately or allow it to cool and thicken for about 10 minutes before using it if you prefer.
Pour the sauce
Place a cookie sheet or wax wrap under the cooling rack to catch any of the dripping sauce.
Use the back of a skewer to poke holes in the cake. Pour the sauce over the warm cake. You can reserve about ¼ cup of sauce to use when serving if you prefer.
Video
Recipe Notes
If you do not have buttermilk, it is very easy to make your own. Simply add 1 ½ teaspoons of lemon juice or vinegar to 1 cup of milk. Set aside for 5 minutes to allow it to curdle before using
You can use either white or brown sugar. I used brown sugar for the amazing caramel, butterscotch flavor it creates.
Cream the butter and sugar well. The air integrated into the mix helps to leaven and create a lighter bake. Beat with an electric or stand mixer for between 3 to 5 minutes on medium-high speed.
Do not overbake. This will cause a dry texture. Remove from the oven when you test with a skewer and see just a few crumbs clinging to it.