Moravian Sugar Coffee Cake

1 pound potatoes, peeled and chopped

2 cups water

½ teaspoon salt

½ cup white sugar

½ teaspoon ground mace

½ cup butter, room temperature

1 egg, room temperature

3 ¼ cups all-purpose flour

2 ¼ teaspoons active dry yeast

1 cup dark brown sugar

1 tablespoon ground cinnamon, or to taste

½ cup chilled butter, diced

2 tablespoons chilled butter, diced

1 teaspoon evaporated milk

Place potatoes and water in a medium saucepan. Bring to a boil. Boil until the potatoes are tender. Drain, reserving 1/2 cup water, and mash. Let cool to room temperature.

Place mashed potatoes, reserved water, salt, sugar, mace, 1/2 cup butter, egg, flour and yeast in the pan of a bread machine in the order recommended by the manufacturer. Select dough cycle; press Start.

Pat dough onto a greased 11x13 inch baking sheet. Cover with a damp cloth and let rise in a warm place until doubled in volume, about 1 hour.

Preheat oven to 350 degrees F (175 degrees C). Combine the dark brown sugar, cinnamon, and chilled butter in a food processor and pulse until butter is the size of coarse crumbs.

Poke several medium holes in the dough and fill with brown sugar and butter. Sprinkle the dough with a few drops of evaporated milk.

Bake in the preheated oven until the cake s edges are golden brown, 20 to 25 minutes.