Step 1
Place potatoes in a small saucepan and cover with water. Bring to a boil then reduce heat and cook covered until soft 10 to 15 minutes. Drain and let cool 15 to 20 minutes. Pass cooled potatoes through a potato ricer and set aside.
Step 2
Stir 3/4 cup plus 1 tablespoon milk and yeast together in a small bowl. Let stand until creamy or foamy about 10 minutes.
Step 3
Combine potatoes yeast mixture flour sugar butter egg lemon zest and salt together in the bowl of a stand mixer. Knead on low speed until dough is smooth elastic and detaches from the bowl about 5 minutes; dough should be slightly sticky.
Step 4
Place dough into an oiled bowl. Turn over to coat. Cover with a damp dish towel and let rise in a warm place until doubled in size about 2 hours.
Step 5
In the meantime mix apple sugar lemon juice and cinnamon for filling together in a bowl. Stir until well combined. Cover and refrigerate filling.
Step 6
Roll dough out on a lightly floured surface into a 12x14-inch rectangle. Spread filling evenly over dough leaving about 1/2 inch free on each long side. Sprinkle with poppy seeds. Roll up tightly lengthwise. Brush seams with a little water and pinch to stick together.
Step 7
Place the roll on a large cutting board seam-side down. Cut into 1 1/2-inch slices using a very sharp knife.
Step 8
Fit rolls loosely into a greased 10-inch round or 9x13-inch rectangular baking pan cut-side down with a little space between them. Cover with a clean towel and let rise in a warm place until visibly doubled in size about 45 minutes.
Step 9
Preheat the oven to 375 degrees F (190 degrees C).
Step 9
Bake in the preheated oven until golden brown 35 to 40 minutes.