Line a wire rack with a thick layer of paper towels or 1 or 2 large paper grocery bags and set near the cooktop.
In a medium bowl, whisk together the sugar, flour, cornstarch, baking powder, and salt.
In a large bowl, whisk together the melted butter, heavy cream, egg, yolk, and vanilla until frothy. Fold the dry ingredients into the wet, using a rubber spatula, until just a few streaks of flour remain. Fold in the apples just to combine.
Fill a large, heavy pot with 2 inches of oil. Attach a deep-fat/candy thermometer to the side of the pot and heat the oil on medium-high heat until the temperature reaches 350°F [185°C], or a bit above.
Scoop 1 1/2-tbsp balls of batter, using a cookie scoop or measuring spoon, and place them in the oil. Fry the fritters for about 2 minutes total, gently flipping them over with wooden chopsticks or any two thin utensils at the halfway point, once one side has browned. Depending on the size of your pot and your patience level, you may fry one fritter at a time or several.
Using a slotted spoon, carefully transfer the fritters to the prepared wire rack. To prevent the fritters from absorbing extra oil, gently pat them with additional paper towels.
Dust with confectioners’ sugar. Apple fritters are best enjoyed warm on the day they are made.