Chill the KitchenAid attachment bowl in the freezer for at least 15 hours.

Whisk egg yolks and 1/4 cup of sugar in a mixing bowl. Heat whole milk in a saucepan until just before boiling. Gradually temper hot milk into egg mixture.

Return mixture to saucepan, add remaining sugar, and heat while stirring until it thickens slightly, about 5-7 minutes. Remove from heat and cool.

Brew strong coffee and let it cool slightly. Mix coffee with the milk and egg mixture.

Combine chilled mixture with heavy cream, vanilla extract, and salt. Stir until smooth. Refrigerate for at least four hours.

Pour the mixture into the chilled KitchenAid attachment bowl and churn on medium speed for 25-30 minutes until soft-serve consistency is achieved.

Transfer soft ice cream to a container and fold in chopped toffee candy. Freeze for at least two hours before serving.