Prepare an ice water bath to cool the ice cream custard.
In a heavy bottomed pot, combine whole milk, cream, 1/2 cup sugar and coffee syrup and coffee granules. Heat over medium heat until just simmering.
Meanwhile, whisk egg yolks with remaining 1/4 cup sugar until light in color; about 1 minute.
Carefully, pour a light stream of the milk mixture into the egg yolks while continuously whisking. If you pour all of the hot milk in at once, you’ll get scrambled eggs. Once they are combined, pour the whole mixture back into the pot. Stir the mixture constantly over medium heat with a wooden spoon. When the custard is finished, it will coat the back of the wooden spoon and when you run your finger down the back of the utensil, the custard will not run. If you have a thermometer, the mixture will be around 175 to 180 degrees. This process could take about 10 minutes to complete.
Pour the custard through a fine sieve or strainer into a large bowl. Place the bowl in the already prepared ice bath and stir to cool. Once the ice cream is cool, place a piece of plastic wrap directly on top of the custard and refrigerate overnight. Prepare the ice cream in an ice cream maker according to the manufacturers instructions, adding the crushed Heath Bar during the last 5 minutes.