Preheat the oven to 325°F (163°C). Line a baking sheet with parchment paper or a silicone baking mat.
In a large bowl, combine the shredded coconut, sweetened condensed milk, lemon zest, lemon juice, and vanilla extract. Mix well and set aside.
In a separate large mixer bowl, add the egg whites and salt. Whip on high speed with the whisk attachment until stiff peaks form.
Gently fold the whipped egg whites into the coconut mixture until fully incorporated.
Drop rounded tablespoons of the coconut mixture onto the prepared baking sheet, spacing them evenly apart.
Bake for 25 to 30 minutes, or until the macaroons are lightly browned on the edges. Allow them to cool completely on the baking sheet.
While the macaroons are cooling, melt the white chocolate according to the package instructions.
Dip the bottom of each macaroon into the melted white chocolate and place it back on the parchment paper to set.
Drizzle the remaining melted white chocolate over the tops of the macaroons and sprinkle with additional lemon zest if desired.
Once the chocolate has set, store the macaroons in an airtight container at room temperature.