Line your 9×13 pan with parchment or foil, lightly greased.

In a very large microwave-safe bowl (8-10 cup capacity), combine sugar, butter, and evaporated milk. Microwave 8 minutes total, pausing every 2 minutes to stir well. The mixture should be bubbling/foamy by the last interval. If not, microwave an additional 1-2 minutes.

Add mini marshmallows and chocolate chips. Stir until completely melted and smooth. If needed, microwave in 30-second bursts to finish melting.

Stir in 1 tsp vanilla until glossy.

Pour into prepared 9×13 pan. Smooth the top. Cool at room temp 1-2 hours, then refrigerate until firm.

Cut into small squares. Freeze if needed.