Preheat your oven to 350°F (175°C). Grease a baking dish or line it with parchment paper.
In a large bowl, combine maize flour, sugar, baking powder, and salt. Mix well.
In another bowl, whisk together melted butter, milk, and vanilla extract (if using).
Pour the wet ingredients into the dry ingredients and stir until well combined.
If desired, fold in raisins or currants.
Pour the batter into the prepared baking dish and smooth the top with a spatula.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Allow the mthochi to cool in the pan before cutting into squares or slices.
Enjoy your meal!