Crack open the eggs in a small bowl along with the milk, brown sugar, vanilla and salt. Mix using a fork until it is all well combined.
Put half the butter on a pan over medium heat on the stove. Take two slices of bread and dip them in the egg mixture, then put them on the pan to cook for about 2-3 minutes each side until lighty golden brown.
Repeat this same step with the other two slices of bread and put aside until needed.
For the roasted banana and garnish:
Slice the banana. In the same pan over medium heat add the remaining butter and then the banana.
Quickly add in the sugar and salt on top of the banana slices and let them cook for 2 minutes until lighty golden and caramelized.
Serve the french toast with a dulce de leche layer and the roasted banana on top. ¡Ready!