Line an 8x8 pan with parchment, leaving an overhang for lifting out later.

Warm the white chocolate chips, sweetened condensed milk, and butter over low heat, stirring constantly until smooth. Remove from the heat.

Stir in the pumpkin puree, pumpkin pie spice, vanilla, and salt until fully combined. Fold in the pecans if using.

Scrape into the lined pan and smooth the top. Chill at least 4 hours, or until firm.

Lift out by the parchment and cut into small neat squares.