Stir together the flour, sugar, yeast, and salt in a large bowl, then add the milk and butter and mix until well blended. Knead the dough for a few minutes until quite smooth. Or, blend the ingredients in a stand mixer fitted with the dough hook, then continue mixing for a few minutes to knead until smooth. Put the dough in an oiled bowl, cover with plastic, and set aside to proof for about 1 hour.
Transfer the dough to a large cutting board and press it out to a roughly 12- by 9-inch rectangle. Arrange the apple slices evenly over and sprinkle the cinnamon over the apples. Roll up the dough and apples lengthwise into a roll. Use a large knife to cut through the dough and apples crosswise at about 1-inch intervals. Then cut across the dough again at an angle (see video above) to cut the dough and apples into small pieces. Reform the mixture into a roughly 12-inch log and repeat the cutting process 2 to 3 more times, until the apples are well chopped and incorporated through the dough. Form the dough into 8 discs about 4 inches across. Arrange them on a rack or baking sheet, cover with plastic, and set aside to proof for about 45 minutes.
For the glaze, stir together the powdered sugar and milk in a small bowl until smooth.
When ready to cook the fritters, put a couple inches of oil in a large Dutch oven and heat to 375°F over medium heat. Gently add 2 or 3 of the dough pieces at a time and cook until well-browned on the bottom, about 3 minutes. Carefully turn the pieces over and brown well on the second side, about 3 minutes longer. If the fritters brown too quickly they may not be cooked all the way through; reduce the heat if needed. Transfer the fritters to a wire rack set over a rimmed baking sheet and continue frying the fritters, reheating the oil between batches as needed.
When all the fritters are cooked, drizzle the glaze over.