Boston - 1 tsp each, ginger and vanilla extract. Catawba - 1 oz. Maple Syrup and 1 oz. Variations Add 2 Tbs Malt powder to shake to make a Malted Milk. Malt is rich in Iron.
Thick shakes depend on the heaviness of the ice cream and the ratio of ice cream to milk.
Experiment with your favorite brand and adjust ratio until you like it. The basic recipe usually is thin, the way a malt and shake is supposed to be. Fruit must be completely crushed and pulpy for chunks of fruit when frozen are like rocks. Add raw egg to shake, almost a perfect food although now raw eggs are risky. Increase heat and bring to boil.