Line a loaf pan with plastic wrap, so the wrap hangs over both the short and long sides of the pan. You may need two pieces of the wrap.
Place the cream, sweetened condensed milk and vanilla in the bowl of a stand mixer fitted with the whisk attachment, and whisk on medium high until medium peaks form.
Position the prepared pan in front of you so the short side is closest to you. Place half of the cream in the pan and begin pressing the wafers into the cream (vertically - so they are standing up like dominos) in short rows that stretch from one of the long sides of the pan to the other.
Continue doing this until you run out of cookies - you will have about 5 short rows. Cover the rows with the remaining whipped cream, smooth the top and refrigerate for 6 to 8 hours.
Flip the pan on to a serving platter, remove it and peel away the plastic. Decorate with rainbow sprinkles and serve.