In a medium bowl, whisk together 1/2 cup sour cream, 1/4 cup granulated sugar, freshly grated zest from 1/2 lime and 1/2 teaspoon kosher salt until well combined. Whisk in 4 large eggs and 1 large egg yolk one at a time, only adding the next egg when the previous one has been fully incorporated. Whisk in 1 cup maple syrup, 1/3 cup fresh lime juice and 1/4 cup heavy cream until the mixture is homogenous.