In a small saucepan stir together sugar and cornstarch; stir in milk, beaten egg yolk and melted butter. Cook and stir over medium heat just until first large bubble appears, then stir vigorously until thickened, about a minute.
Remove from heat, strain, then stir in vanilla. Pour mixture into molds and insert sticks. Freeze until firm, about 4 hours.
Run molds briefly under warm water to release pops.
Notes
This makes about 4 pops, depending on your molds. Double or triple for a crowd. I used allulose sweetener and had no problem with crystallization I used 2/3 cup reduced fat milk and 1/3 cup cream. Feel free to use the combo of dairy/non-dairy milk and/or fat/low-fat milk/cream that suits your diet, though creaminess of the final product will vary.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.