Line an 8-inch square pan with parchment, leaving overhang for lifting.
Combine white chocolate chips, condensed milk, and butter in a heavy saucepan.
Warm over low heat, stirring constantly, until melted and smooth.
Remove from heat; stir in vanilla and salt until fully blended.
Fold in almonds if using, then spread mixture into the prepared pan.
Smooth the top and scatter sprinkles over the surface, pressing lightly.
Chill until firm, about 2 hours. Lift out and cut into small squares.