Mix the soft butter with the manjar blanco until uniform. You can do it by hand or using a mixer.
Add the salt, egg and egg yolk and mix once again.
Add the flour using a spatula and mix until uniform.
Butter the ramekins and then flour them. Make sure to remove the excess by tapping them.
Fill them up leaving 3mm without dough and then take to the fridge for at least 1 hour and up to 3 days. This helps to decrease the risk of having a cooked center.
Take them to a preheated oven at 200C for 12min. This time will vary depending on your oven, so try making one first and see how it comes out. Then adjust the time accordingly for the rest of them. Remember that 1 minute will make a lot of difference in the result.
Run a thin knife around the lava cake and turn onto a plate as soon as they come out of the oven because they keep cooking inside the ramekin even out of the oven.
Serve immediately with vanilla ice cream.