In a nonstick pan, melt the chocolate and sweetened condensed milk over low heat until a shiny mixture forms. Add butter and stir until combined. Turn off the heat.

Scoop the fudge with a tablespoon onto a parchment-lined baking sheet, forming ~30g balls. Freeze. You only need 6 for the cookies.

Use an electric mixer to whisk butter and sugar until light and creamy (2-3 minutes). Add the egg and whisk for 30 seconds.

Stir in the dry ingredients, using a spatula to combine. Stop mixing once everything comes together.

Place the cookie dough in the freezer for 10 minutes.

Preheat the oven to 375°F.

Divide the chilled dough into 6 equal parts (about 75g each).

Roll each into a ball. Flatten in your palm, place a frozen fudge ball, and seal with cookie dough. Roll into a ball.

Place the 6 cookie balls on lined baking sheets, leaving space to spread.

Bake at 375°F for ~12-13 minutes. Cookies should be semi-firm to touch; they'll firm up more after baking.