Combine sugar with constarch and salt in a glass bowl. Whisk in milk until smooth. Microwave on high for 1 1/2 to 2 minutes or until mixture comes to a boil and thickens. Stir at least once during cooking. Beat eggs lightly.
Stir some of the hot sauce into egg, then whisk warm egg back into custard. Microwave on medium for 20 to 40 seconds or until thickened. Whisk until smooth.
Whisk in vanilla and set aside.
Preheat oven to 400 degrees.
Roll half the pastry on a lightly floured surface into a 12-x 8-inch rectangle. Cut pastry into six 4-inch rectangles. Transfer to rimmed baking sheet lined with parchment paper. Repeat with remaining pastry. Slice peaches thinly. Toss gently with blueberries, lemon juice and sugar.
Spoon fruit mixture into centre of pastry rectangles. Top fruit with about 2 teaspoons of custard and a small pinch of nutmeg. Bake for 20 minutes, rotating pan after 10 minutes. Pastry should be puffed and golden.
Cool slightly on racks. Serve danishes with remaining custard on the side.
Adapted from Homemakers Magazine Summer 2002