Preheat oven to 400 degrees F. Pour the milk into the bowl of a heavy-duty mixer fitted with a dough hook. Sprinkle the yeast over it and wait until the yeast dissolves, about 5 minutes. Add the olive oil and egg, then the flour and salt. Knead at medium speed until the liquid is absorbed, then continue kneading for 6 minutes, adding additional flour or water if needed. The dough should form a ball on the hook. It will be soft and smooth. Cover the mixer bowl with plastic wrap and let stand at room temperature (75 degrees F) until the dough doubles, about 2 1/2 to 3 hours. Turn out the dough onto a well floured work surface. Divide it into 6 pieces. Shape each piece into a tight round ball. Cup your fingers over the dough and push it against the table with your palm in a circular motion. If it slides on the table, brush the flour off the table, lightly sprinkle the table with water and try again. Put the rounds on a parchment lined baking sheet, let rest a few minutes, then flatten each one with your outstretched fingers. Then put the sheet into a large plastic bag. Let stand in a warm room (75 to 80 degrees F) until the rounds double in size and will hold a finger imprint, about 1 1/2 hours. Remove the baking sheet from the plastic bag. Gently brush each bun with water and sprinkle sesame seeds or poppy seeds on top. Bake until golden brown and hollow sounding when thumped on the bottom, about 25 minutes. Cool on a rack. If the buns are too tall for the burgers, cut a disc from the middle before assembling. Yields 6 buns.