Preheat the oven to 325°F. Line two baking sheets with parchment paper.

In a large bowl, stir together the sweetened condensed milk, fresh lime juice, lime zest, egg white, vanilla, and salt until evenly combined.

Add the sweetened coconut and mix thoroughly until the coconut is evenly coated and the mixture holds together when pressed.

Using a spoon or a 2-tablespoon cookie scoop, portion the mixture into mounds (about 2 tablespoons each) and shape each mound with a slight peak. Place the mounds on the prepared baking sheets about 2 inches apart.

Bake for 15 to 20 minutes, or until the macaroons are set and slightly golden brown. If you bake both sheets at once, rotate them between racks halfway through baking for even color.

Remove the baking sheet from the oven and cool the macaroons on the sheet for 5 minutes. Transfer the macaroons to a cooling rack and cool completely before coating.

Place the chopped white chocolate in a microwave-safe bowl. Microwave in 20-second increments, stirring after each interval, until the chocolate is melted and smooth.

Lay out a piece of wax paper. Dip the bottom of each cooled macaroon into the melted white chocolate so only the bottoms are coated; let excess chocolate drip back into the bowl and set the dipped macaroons chocolate-side down on the wax paper.

Use any remaining melted chocolate to drizzle over the tops of the macaroons (use a spoon or fork). Allow the chocolate to set completely at room temperature before serving or storing.