Step 1
Combine sugar and yeast in a bowl. Pour in milk butter and egg. Whisk together until sugar is dissolved. Stir in flour a portion at a time until mostly moistened adding more if dough is too wet. Add salt and stir until a soft slightly sticky dough comes together.
Step 2
Cover dough with a damp towel and let rise in a warm spot until doubled in volume about 1 1/2 hours.
Step 3
Grease a 9x13-inch baking dish with 1/2 tablespoon butter. Split peaches in half along the seam and slice halves into quarters then eighths.
Step 4
Transfer dough into the buttered baking dish. Use a spatula to spread dough out to the corners of the dish. Cover with plastic wrap and let rise once more until roughly doubled in volume 30 to 45 minutes.
Step 5
Preheat the oven to 375 degrees F (190 degrees C).
Step 6
Arrange peach slices onto the dough pressing them in lightly. Drizzle remaining butter on top. Sprinkle Demerara sugar over peaches.
Step 7
Bake in the preheated oven until a toothpick inserted into the cake not through a peach comes out clean 40 to 45 minutes.
Step 8
Heat apricot preserves up with a splash of water and brush glaze over the top of the cake. Let cool to room temperature before slicing.