Line an 8 x 8-inch square tin with parchment. Spray generously with nonstick spray.

Melt the chocolate over a bain marie or double boiler.

Whisk in the sweetened condensed milk, and continue whisking until thick and creamy.

Remove from heat. Allow chocolate to cool for 3-5 minutes, then whisk again.

With a plastic or wooden spoon, stir in the mini marshmallows.

Pour mixture into prepared tin. Use a greased rubber spatula to distribute the fudge equally across the surface of the tin, and push it into the corners. Tap the pan on the countertop to help the mixture settle.

Transfer to the refrigerator to chill for at least one hour.

Remove fudge slab from the tin and use a sharp, oiled chef’s knife to cut it into squares. I cut mine into 36 pieces (6 rows x 6 rows) but feel free to make your fudge squares as large or small as desired.

Store leftover three ingredient fudge in the refrigerator in an airtight container for up to two weeks.