Preheat your oven to 350°F (180°C). Grease a 9-inch round cake pan with butter and dust lightly with cornmeal to prevent sticking.

In a large mixing bowl, cream together the softened butter and sugar using a wooden spoon or hand mixer until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each addition until fully incorporated.

In a separate bowl, whisk together the cornmeal, all-purpose flour, baking powder, and salt.

Gradually add the dry ingredients to the butter mixture, alternating with the milk. Begin and end with the dry ingredients, mixing just until combined after each addition.

Stir in the vanilla extract until evenly distributed throughout the batter.

Pour half of the batter into the prepared cake pan, spreading it evenly.

Cut the guava paste into small cubes (about 1/2 inch) and distribute half of them over the batter in the pan.

Pour the remaining batter over the guava layer and smooth the top. Scatter the remaining guava paste cubes on top.

Bake for 38-42 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown.

Remove from oven and let cool in the pan for 10 minutes before transferring to a cooling rack.

Slice and serve warm or at room temperature.