In large bowl, dissolve 1 tsp/5 mL of the sugar with 1/4 cup/60 mL warm water; sprinkle in yeast. Let stand until frothy, about 10 minutes.

In saucepan, heat together milk, butter, salt and remaining sugar until butter is melted; when lukewarm, whisk into yeast mixture. Whisk in egg. Stir in flour to make soft ragged dough. Turn out onto lightly floured surface; knead, adding more flour as necessary if dough is sticking, until smooth and elastic but still quite soft, about 10 minutes.

Place in large greased bowl, turning dough to grease all over. Cover with plastic wrap; let rise in warm place until doubled in bulk, about 1-1/2 hours.

Meanwhile, blanch and drain spinach, squeezing out excess moisture; chop finely and set aside.

Gently push down dough; transfer to lightly floured surface. Lightly knead into ball; press into square. Cover and let rest 10 to 15 minutes. Roll dough into about 20- x 10-inch/50 x 25 cm rectangle, long side at bottom.

Leaving a 1-inch/2.5 cm border at top and bottom, spread dough evenly with spinach and top with cheese; from bottom, roll up into cylinder, pinching together edge. Slice into 12 equal pieces.

Place rolls, seam side down, in buttered muffin cups; cover with tea towel and let rise in warm place until doubled in bulk, about 1 hour. Whisk yolk with 2 tsp/10 mL water; brush over rolls.

Bake in centre of 375°F/190°C oven until dough in centre is fully cooked and tops are nicely browned, 18 to 20 minutes. Let cool in pan on rack for 5 minutes; remove from pan and cool on rack. Serve warm or fully cooled.

Makes 12 rolls.

Blanching How-Tos

Use one of two methods.

Bring a very large pot of lightly salted water to a rolling boil; add cleaned spinach and cook just until water returns to boil (this should take only a minute or so). Drain; chill under cold water and drain well.

For most household stoves (except for induction cooktops), it is a waste of energy to bring a huge pot of water to a boil, so use the steam-blanching method, instead. place cleaned spinach with water clinging to it in a large pot. If the spinach isn't very wet, add enough water to come scant 1/2-inch/1 cm up side of pot. Sprinkle with a pinch of salt. Cook over high heat, covered and stirring once, until wilted. Drain; chill under cold water and drain well.