Preheat the oven to 350°F. Begin by combining desiccated coconut and flour in a bowl. Set aside.
In a separate bowl, cream butter and sugar with an electric mixer or by hand.
Add egg yolk one at a time and mix well. Then, pour in condensed milk and mix again.
Use a large rubber spatula to fold the wet mixture into the coconut mixture. Mix until well combine.
Arrange the macaroon cups on a baking sheet and fill each cup to half.
Bake for 25 to 30 minutes until the tops are golden. Let cool on the pans for a few minutes, then transfer to a wire rack to cook completely.