Mix ½ cup milk, 1 teaspoon granulated sugar, and 2 teaspoons active dry yeast in a glass. Let it rest in a warm spot for about 10 minutes, until foamy.
In the bowl of a stand mixer fitted with the dough hook, combine 3 cups all-purpose flour, ⅓ cup milk (lukewarm), 1 egg, 4 Tablespoons unsalted butter (not hot), 3 Tablespoons granulated sugar, and ¼ teaspoon salt. Add the activated yeast mixture.
Knead on medium speed for about 10 minutes, until the dough is smooth, elastic, and only slightly sticky.
Shape the dough into a ball and place it in a clean bowl. Cover with plastic wrap and let it rise in a warm spot for about 1 ½ hours, until doubled.
Divide the dough into 10 equal pieces and shape them into bones, souls, or vertebrae (see Notes).
Line a baking sheet with parchment paper and arrange the shapes about 1.5 inches (4 cm) apart. Cover with a tea towel and let rise for 30 minutes. Toward the end of the rise, preheat the oven to 390 °F.
Brush the risen shapes with ½ egg (beaten) and sprinkle with 2 teaspoons poppy seeds, if using.
Bake for about 15 minutes, until golden brown. Let the rolls cool briefly before serving.
Notes
Milk: lukewarm means about 100°F (37°C), barely warm on the wrist. Hot milk kills the yeast.
Shapes: for bones, roll a rope and lay it in a gentle S, or thin the rope in the middle, cut into both ends, and spread them apart. For souls, twist two ropes together and join them into a small ring. For vertebrae, set four small balls in a row so they touch.
Sealing: press the ends of twisted shapes together firmly, or they open up in the oven.
Oven: temperatures are for a conventional oven; for convection, lower by 25°F.
Store: airtight at room temperature for 3 days, or freeze for up to 3 months.