Whisk the mango pulp, sugar, lemon juice, cornstarch and salt in a medium saucepan. Whisk in the egg yolks.
Cook the mixture over medium heat, whisking constantly, until it¿s thick like pudding, 5 to 7 minutes. Remove from the heat and whisk in the butter a few pieces at a time until incorporated.
Strain the mixture through a fine-mesh sieve into a small bowl, pushing it through with a rubber spatula. Press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate until completely set, at least 4 hours and up to 5 days.