Check if your ice cream machine bowl needs to go in the freezer, in which case freeze a couple of hours before starting the custard.
In a large bowl, mix together the egg yolks and caster sugar. Pour the milk and double cream into a large saucepan over a medium heat. Bring up to just before boiling then take off the heat and slowly pour onto the egg yolk mix, stirring together to combine. Return the mixture to a clean large saucepan and heat gently while stirring until it reaches 82°C.
Once up to temperature, pour into a clean bowl and leave to cool slightly for 10 minutes. Stir in the baileys and then leave to cool further until room temperature before refrigerating for an hour. Meanwhile, make the base.
Melt together the butter and chocolate in a heatproof bowl over a pan of simmering water. Meanwhile blitz the speculoos biscuits in a food processor until they are a fine crumb.
Once the butter and chocolate are completely liquid, pour them into the blitzed up biscuits and then pulse 4-5 times until it’s well mixed. Spoon the base mixture into the pie dish, and using the back of the spoon, press evenly around the base and up the sides. Put in the freezer to chill for 20 mins.
Once the base is set, churn the ice cream according to your ice cream machine’s instructions and then spread the ice cream over the base and smooth the top down with a palette knife or a spoon until level.
Cover closely with cling film and return the whole pie to the freezer to firm up for at least 1 hour, or overnight.
Make the caramel. Pour the golden syrup in a medium pan along with the sugar. Bring to the boil over a medium-high heat and let it bubble for 4-5 minutes until it has turned a slightly darker golden shade.
Take off the heat and whisk in the Baileys, double cream and butter until it has all come together. Careful as this may spit. Pour into a heatproof bowl and leave to cool at room temperature.
When ready to serve, take out of the freezer and pour on the caramel, smoothing with a palette knife. Sprinkle with sea salt and cut into 8 wedges.