Combine heavy cream, milk, salt, and half of the sugar in a pot. Heat over medium heat until scalded. Do not boil. Remove from heat and set aside.
In a small bowl combine egg yolks and rest of the sugar. Whisk until incorrporated.
Temper the eggs. Using a measuring cup, remove 1/2 a cup of the milk mixture. LIttle by little pour the milk into the egg mixture while constantly whisking. Add the milk very slowly or the egg yolks may cook too much and become scrambled eggs.
Very slowly pour the warmed egg yolks back into the milk mixture. Heat over medium heat (do not boil) until thickened into a custard and the mixture coats the back of a wooden spoon. Remove from heat.
In a small bowl, heat treacle in the microwave for 5-7 seconds. Pour into the custard mixture and stir until well combined.
Transfer to a bowl, cover and chill in the refridgerator until completely cold.
Churn mixture in a ice cream maker according to appliance directions (about 20 to 30 minutes.) Transfer to a storage container, cover with plastic wrap and freeze until ready to serve.
