In a blender, blend the eggs, the sugar, the milk and the butter, blend until combined.
Transfer the mixture to a bowl, add the wheat flour gradually and using a whisk, mix. Add the rest of the flour and mix well until combined, add the baking powder and mix.
Grease a cake pan with butter and flour, pour half of the batter, add half of the guava paste cut into cubes, add the rest of the batter and the rest of the guava paste.
Bake in a preheated oven at 180°C (356°F) for 50 minutes (do the toothpick test).
Into a pan, add the guava paste cut into larger pieces, add the water and leave the heat on medium temperature, when the guava starts to melt, stir non-stop until it melts completely.
Let the guava syrup cool, unmold the cake and pour the syrup all over it.