Line an 8×8 inch square pan with parchment paper or aluminum foil, leaving an overhang on the sides so you can lift out the fudge easily after it’s set.
Place your chocolate chips in a heat‑proof bowl. Using a double boiler (or placing the bowl over simmering water), melt slowly, stirring frequently until smooth. Be careful not to let water or steam drift into the chocolate (that can seize it).
Once the chocolate is melted, remove from heat and stir in the sweetened condensed milk and vanilla extract until fully incorporated.
Gently stir in the Fireball cinnamon whiskey until fully blended into the chocolate mixture.
Transfer the fudge mixture into the lined 8×8 pan. Use a spatula to spread evenly and smooth the top.
Cover the pan (with plastic wrap or foil) and place into the refrigerator. Let it chill for at least 2 hours (some recommend 3+ hours or overnight) until firm.
Once firm, lift the block out using the parchment/foil overhang, then cut into squares (or festive shapes). Serve and enjoy.