Line an 8-inch square pan with parchment paper, leaving a little overhang.

In a saucepan over low heat, combine sweetened condensed milk, semi-sweet chocolate chips, butter, and a pinch of salt.

Stir slowly and constantly until melted and glossy.

Remove from heat and stir in vanilla extract.

Pour mixture into the lined pan and tap gently on the counter to level it.

For a white chocolate swirl, melt white chocolate chips separately, drizzle on top and swirl with a butter knife.

Sprinkle holiday toppings on top immediately so they stick.

Chill in the refrigerator until firm, then slice into squares.