Preheat the oven to 325°F (163°C). Line two cookie sheets with parchment paper or silicone baking mats.
In a large bowl, stir together the sweetened condensed milk, egg white, vanilla, and salt until combined.
Fold the flaked coconut into the wet mixture until the coconut is evenly coated and the mixture holds together.
Drop tablespoonfuls of the mixture about 2 inches apart onto the prepared sheets, forming loose haystack shapes with moistened fingertips as needed to prevent sticking.
Bake one sheet at a time until the macaroons are light golden brown, 15 to 20 minutes. Let cool on the baking sheet for about 2 minutes, then transfer to a wire rack to cool completely.
To dip, set a small heatproof bowl over a pan of simmering water and melt 8 ounces of the chopped semisweet chocolate, stirring until smooth. Remove from heat and stir in the remaining 2 ounces of chocolate until fully melted and glossy.
Hold each macaroon by the pointed top and dip the bottom and about 1/2 inch up the sides into the melted chocolate. Scrape off excess and place on a prepared baking sheet.
Refrigerate the dipped macaroons until the chocolate sets, about 15 minutes.