Grease a 8" tin and line the base only. Preheat oven to 160C. Melt the sugar in a saucepan over medium to low heat. Stir until all the sugar has melted. Turn off the heat and add 2 cups of water. Set aside to let it cool.
Cream butter and condensed milk till well combined. Add in eggs one at a time on low speed. Sift in flour and mix well using low speed. Add in cooled syrup and baking soda and stir.
Pour into prepared baking tin and bake till skewer comes out clean. (Mine took about 1 hour 30 minutes)