To prepare a tarta tres leches recipe, first you need to prepare the filling. First, you will need the following ingredients: 1 cup (240 milliliters) of heavy cream, 2 tablespoons (2.5 ml) sugar, 1 teaspoon (0.02 g) vanilla extract, and 1 tablespoon (0.5 tsp) salt. Mix the ingredients together until they are well combined. Pour the mixture into the tart shell and bake it in the oven for 20 to 25 minutes or until the top is golden brown.