1Juice mango through the low-pulp screen. You should end up with about 1/2 cup of mango juice.
2In a non-reactive stainless steel bowl, whisk together egg, egg yolks, and sugar until light and frothy. Whisk in mango juice, lime juice, and salt. Set bowl over (but not touching) a pot of gently simmering water, and whisk gently for about 12 to 15 minutes, or until mixture thickens enough to coat the back of the spoon (approximately 170ºF on a thermometer).
3Remove bowl from heat and whisk in butter, a little at a time, until fully incorporated. Press through a fine mesh sieve to remove any stray solids. Transfer to a storage container and cover, pressing plastic wrap onto the surface of the curd to prevent a skin from forming. Refrigerate for at least 1 to 2 hours until set. Curd will keep, tightly covered in the refrigerator, for up to 2 weeks.