One of the best proteins that will mix up like a pudding is the Supreme Pea Protein. For the right thickness, use less water than you would to make a shake. It's best to use an electric blender to mix it, but a handshaker will also work. If chilled is your preference, after mixing, place it in a bowl in a fridge for 30 minutes, and it comes up like a dessert.
The other option is Pure NZ Casein. When mixed with smaller amounts of water it comes up very, very thick, like a mousse or pudding. An electric blender is recommended for mixing this thickness, but like the Supreme Pea Protein, you can use a handshaker. For flavour, you can add some Flav A Shake flavouring powder, or mix it 50:50 with your Defining Whey Premium.