Place a pot on top of another pot with simmering water. Make sure the water doesn't touch the upper pan. Add condensed milk and chocolate chips to the pan on top. This is called the double boiler method. You may also melt the chocolate and condensed milk together in a microwave.
Stir till the chocolate melts, then add mexican vanilla extract, cayenne pepper and cinnamon powder. Whisk till combined and chocolate is completely melted and smooth.
Transfer mixture to a 8 or 9 inch square pan lined with parchment paper. Use a spatula to spread the chocolate throughout the pan.
Top with mini marshmallows.
Cover and keep the pan in the refrigerator till the fudge sets, around 3-4 hours. Cut into pieces and enjoy!