Preheat your oven to 350°F (175°C). Grease an 8-inch square baking pan or a round cake pan.
In a large mixing bowl, combine the flour, granulated sugar, baking powder, and salt. Mix well.
Cut the cold, cubed butter into the flour mixture using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
In a separate bowl, combine the milk, water, and vanilla extract. Gradually add this mixture to the flour mixture, stirring until a dough forms.
Pour the dough into the prepared baking pan and spread it evenly.
Bake in the preheated oven for about 30-35 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Allow the Johnny Cake to cool in the pan for a few minutes before transferring it to a wire rack to cool completely.
Slice and serve as a side dish with butter or jam, or alongside savory dishes.
Enjoy your meal!