Preheat the oven to 180–200°C and line a 20×20 cm pan with baking paper.
Grind the Lotus biscuits into fine crumbs.
Transfer the crumbs to a bowl and mix with the baking powder.
Pour in the hot milk and stir until the mixture is smooth and evenly combined.
Pour the batter into the prepared pan and spread it evenly.
Bake for about 30 minutes, or until the cake is set in the center.
Let the cake cool completely in the pan.
Melt the Biscoff spread using a bain-marie or short microwave bursts, then pour it over the cooled cake.
Decorate with extra crushed Lotus biscuits if desired.
Slice into squares and serve.