Line one or two baking sheets with waxed paper or parchment. Keep the marshmallows cold, or place them in the freezer briefly while preparing the chocolate-coconut mixture.

Melt the butter in a saucepan over medium heat. Stir in the sugar, evaporated milk, and cocoa powder until the mixture is smooth and evenly combined.

Bring the mixture to a steady boil while stirring constantly. Boil for about 5 minutes, watching carefully so the chocolate mixture does not scorch.

Remove the saucepan from the heat and stir in the vanilla extract and 3 cups of shredded coconut. Mix until the coconut is thoroughly coated.

Let the mixture cool for about 20–30 minutes, or until it is firm enough to handle but still pliable. If it becomes too firm, warm it very briefly or mix in 1 teaspoon of evaporated milk.

For each cookie, flatten a portion of the chocolate-coconut mixture in your palm. Place one large marshmallow in the center, or use miniature marshmallows for smaller cookies, then wrap and seal the mixture completely around the filling.

Roll each wrapped cookie in extra shredded coconut if desired. Arrange the cookies on the lined baking sheets with a little space between them.

Freeze or chill the cookies for 1–2 hours, or until firm. Store them frozen or refrigerated, and allow them to soften slightly before serving.