In small saucepan, whisk 1/4 cup/60 mL of the bread flour with 3/4 cup/175 mL cold water over medium-low heat. Cook, stirring, until thickened and thermometer inserted in centre of mixture registers 150°F/65°C (or ridges form and keep their shape after every stir). Scrape into bowl; cover with plastic wrap directly on surface. Refrigerate for 2 hours or for up to 2 days. Bring to room temperature before use.

In large bowl, stir sugar into 1/2 cup/125 mL warm water until dissolved; sprinkle with yeast. Let stand until foamy, 5 to 10 minutes. Scrape starter and sour cream into yeast mixture; stir until smooth. Stir in spelt flour and salt; stir in remaining bread flour until shaggy dough forms.

Knead, adding up to 1/2 cup/125 mL more bread flour as necessary, until dough is smooth, moist and slightly sticky. (This dough needs more kneading than most, so knead slowly and steadily with patience.) Form into ball; place in greased bowl, turning to coat. Cover; let rise in warm place until doubled in bulk, about 1-1/2 hours.

Lightly punch down dough; knead lightly for a few turns. Halve dough; form each half into ball. Cover; let rest for 10 minutes to relax the gluten.

With sharp knife, cut each ball into 8 equal pieces; form each piece into ball, pulling down sides and pinching into bottom at centre. Place, evenly spaced, on lightly buttered baking sheet. Brush tops with butter. Cover; let rise in warm place until doubled in bulk, about 45 minutes.

Bake in centre of 375°F/190°C convection or 400°F/200°C conventional oven until golden, 22 to 25 minutes. (To test if rolls are cooked, insert knife into centre roll for 5 seconds; remove. If blade is clean and hot, rolls are done.) Let cool in pan on rack.

Makes 16 rolls.