Christmas Fudge

 3 Tbsp. unsalted butter, cubed, plus more for pan
 2 1/2 cups dark chocolate chips (about 14 oz.; 60% to 70% cacao)
 1 (14-oz.) can sweetened condensed milk
 1 tsp. pure vanilla extract
 1/2 tsp. kosher salt
 2 to 3 Tbsp. Christmas sprinkles

Butter an 8″ x 8″ baking pan and line with parchment, leaving a 2”
overhang on 2 opposite sides. In a medium saucepan over medium heat,
cook butter, chocolate chips, milk, vanilla, and salt, stirring constantly
with a rubber spatula, until chocolate is melted and smooth, about 5
minutes. Pour into prepared pan. 
Top with sprinkles. Refrigerate until set, at 2 hours and up to 1 day. 

Run a sharp knife around edges of pan. Using parchment overhang, lift out
fudge and transfer to a cutting board. If fudge is difficult to remove, wait 5
minutes until it warms slightly and try again. Cut into small squares (about
1 ½ inch squares