Cut 14 oz guava paste into small cubes (You can skip this step but it will make softening the paste on the stove easier.)
Add the cubed guava paste to a small saucepan with 1/2 cup water over medium-low heat until softened, about 10 minutes. Stir the guava occasionally, breaking up bits until you have a jam-like consistency. Allow the guava to cool completely.
Separate 5 egg yolks and put them in a large bowl. Save the egg whites for later. We won’t be needing them in this recipe.
Whisk together 5 egg yolks and 1/4 cup sugar in the large bowl with a hand mixer until it’s a pale yellow color.
Add 8 oz mascarpone to the egg and sugar mixture and mix.
Add half of the softened guava paste (make sure it's cooled) to the mascarpone, egg, and sugar base. Mix it together. It should have a muted pale pink color. Make sure to save the other half of the guava; we’ll be using it later. Transfer the guava mascarpone mixture to the fridge while you make the whipped cream.
In a separate large bowl, whip 2 cups heavy cream with a hand mixer until it becomes a whipped cream.
Fold the whipped cream into the guava mascarpone mixture.
Put the cream mixture bowl back in the fridge while you prepare the ladyfingers.
In another bowl, whisk together 1/2 a 14 oz can of sweetened condensed milk, 1/2 a 12 oz can of evaporated milk, and 1 cup whole milk. Whisk until the condensed milk is fully incorporated into the other milk. This is your tres leches mixture.
Dip ladyfingers in your tres leches mixture for a second or two — don’t oversoak them. Line the bottom of the pan with the dipped lady fingers until completely covered. Only dip as many ladyfingers as you need to cover the bottom of the pan.
Spread half of the reserved softened guava paste onto the ladyfingers in an even layer with a spatula, making sure there’s guava in every bite.
Take your reserved cream mixture from the fridge and pour half of it on top of your ladyfingers with guava. Smooth it out with a spatula. (If you want a taller tiramisu, pour less than half of the mixture so the majority of the cream sits on top). Soak the remainder of the ladyfingers and build your second layer the same way you built your first.
Spread the rest of the guava paste on top of the ladyfingers.
Add the remaining amount of cream on top of the second layer of lady fingers. Smooth it out.
Transfer your tiramisu to the fridge to set for at least 12 hours.
Before you take the tiramisu out of the fridge, crush 6-12 Maria cookies in a Ziploc bag with a rolling pin into a fine dust.
After 12 hours, take the tiramisu out of the fridge and dust the crushed Maria cookies on top.
Once the Maria cookie dust covers the tiramisu, it’s ready to serve and enjoy.