First, get your mangoes peeled, pitted, and pureed. You'll want about 1.5 cups of smooth mango puree. In a separate medium heatproof bowl, whisk together the granulated sugar, whole eggs, egg yolks, and salt until light in color and well combined. Set aside.

Pour the mango puree into a medium saucepan and heat it over medium-low heat until it just begins to simmer around the edges, about 3-5 minutes. Don't let it boil vigorously.

Carefully ladle about half of the warm mango puree into the egg and sugar mixture, whisking constantly to prevent the eggs from scrambling. This step is called tempering, and it slowly brings the eggs up to temperature.

Pour the tempered egg mixture back into the saucepan with the remaining mango puree. Return the saucepan to medium-low heat and cook, whisking constantly, until the mixture thickens enough to coat the back of a spoon, about 8-12 minutes. The curd should reach about 170°F (77°C) on an instant-read thermometer. Don't let it boil.

Remove the saucepan from the heat. Stir in the softened butter pieces, one at a time, until fully melted and incorporated. Then, whisk in the fresh lemon juice and lemon zest.

For the smoothest curd, press the mixture through a fine-mesh sieve into a clean heatproof bowl. Cover the surface directly with plastic wrap to prevent a skin from forming, then refrigerate for at least 4 hours, or preferably overnight, until thoroughly chilled and set.