In a large bowl or pitcher, whisk together the whole milk, sweetened condensed milk, heavy cream, pudding mix, malted milk powder, caramel sauce, vanilla, and salt. Whisk a full minute until no lumps of pudding powder remain and the caramel is fully dissolved.
If your ingredients were not cold to start, refrigerate the mixture at least 1 hour.
Pour the mixture into the Ninja Slushi vessel, staying between the minimum and maximum fill lines.
Select the MILKSHAKE preset and leave it at the default temperature. The unit will beep three times when it reaches target texture, typically in 45 to 60 minutes.
Dispense within 30 minutes of the beep to avoid a foamy texture.
Drizzle caramel inside a clear cup, dispense the Frosty, add toffee bits, dispense more Frosty, and finish with caramel and a scatter of toffee.