Peel the guavas. Cut them in small slices and place them in a pan with the water and half of the Le Zuc. Boil for 35 min on high heat. Sieve the mixture and place it again over the fire on medium heat. Add the lemon juice, salt and the rest of Le Zuc, continue to cook until it thickens.
Mix the sugar and the eggs until stiff, immediately add the yolks and vanilla. Sieve the flour, salt and baking powder twice. Add the sieved powder in a progressive way to the previous mix. Spread the mixture into the mold that was previously coated with waxed paper and bake at 350°F for 10 to 12 minutes.
Remove the paper and unmold the cake onto a damp cloth, roll it and let it cool. Stuff with guava jam and roll again. Sprinkle with a little bit of Le Zuc.