Place the flour in a large bowl and form a well.
Add the softened butter, 1 beaten egg, sugar and salt.
Gradually add the flour to the mixture, then add the water little by little until you get a homogeneous dough.
Form into a ball, cover and leave to rest for 30 minutes in the refrigerator.
Dice the guava paste and place it in a saucepan with the water.
Heat over low heat, stirring, until you get a smooth and homogeneous filling. Set aside and let cool.
Divide the dough into two equal-sized pieces.
Roll out the first piece of dough thinly on a lightly floured work surface.
Line a buttered 20 cm diameter round pie pan.
Pour the guava filling over the pie crust and spread evenly.
Roll out the second piece of dough and cut thin strips of dough.
Arrange the strips on the pie in criss-cross shapes.
Brush the dough with the second beaten egg.
Bake at 180°C for 40 minutes, until the pie is golden brown.
Let cool before removing from the pan and serving.