Heat oven to 180C/fan 160C/gas 4 and line two large baking sheets with baking parchment. Put the peanut butter, sugar, ¼ tsp fine table salt and chocolate chunks in a bowl and mix well with a wooden spoon. Crack in the egg and mix again until the mixture clumps together and forms a dough.

Break off chunks of dough (about the size of a cherry tomato) and arrange them, spaced apart, on the sheets. Press the cookies down with the back of a fork to squash them a little. (The cookies can be frozen for up to two months – to cook from frozen, add an extra 1-2 mins to the cooking time.) Bake for about 12 mins until golden around the edges and paler in the centre. Leave to cool on the trays for 5 mins.

Meanwhile, put the bananas, cream and vanilla in a food processor and blend until they make a thick ice cream. Scoop into balls with an ice cream scoop, and sandwich between the cookies. Serve immediately.