To make mango puree, peel mangoes and dice into small pieces. Place in a small saucepan with 1/4 cup of water and simmer until the mangoes soften—3-5 minutes. Transfer to a blender and blend until smooth, then pass through a fine mesh sieve to remove the fibers.

In a double boiler, add 2 inches of water and bring to a boil. Reduce heat to medium-high, then combine sugar and mango. Stir semi-frequently, until the sugar dissolves and the puree is hot to the touch.

In a medium mixing bowl, whisk together the yolks, egg, salt, and lemon juice. Add hot mango puree 1 Tbsp at a time until the eggs are tempered.

Return to double boiler and stir frequently for 15-20 minutes, or until the curd thickens and begins to set. If you desire a thicker curd, you may leave it on for more time.

Once the curd thickens and can coat the back of a spoon and just hold its shape, remove from the heat; it will continue to set off heat. Add the orange zest and butter, one pat at a time, then transfer to a jar and allow to cool, covered, at room temperature. Transfer to the refrigerator and keep for up to 2 weeks.