Preheat the oven to 400 degrees F (200 degrees C). Grease a 9-inch round cake pan generously with 1 teaspoon butter, and place a circle of parchment in the bottom. 

Whisk egg and sugar together in a bowl until light and fluffy, about 1 minute. Whisk in melted butter, yogurt, and milk until combined.

Add cornmeal, flour, salt, baking powder, and baking soda to egg mixture; whisk until dry ingredients are moistened. Fold in 2 cups of the cornflakes with a spatula. Transfer batter to the prepared pan, and smooth the top.

Scatter remaining 1/2 cup cornflakes evenly over the top; press in lightly with your fingers.

Bake in the preheated oven until a skewer inserted near the center comes out clean, about 25 minutes.

Cool cake in the pan for 15 to 20 minutes before removing to a plate. Cool completely before serving with fresh fruit or a fruit sauce.