Activate yeast – Combine warm milk and a pinch of sugar; sprinkle yeast on top and let stand 5–10 min until foamy.
Make dough – In a large bowl whisk flour, remaining sugar, and salt. Add yeast mixture, melted butter, and egg; stir to a shaggy mass.
Knead – Turn onto a floured surface; knead 8–10 min until smooth and elastic.
First rise – Place dough in a greased bowl, cover, and let rise 1 hour or until doubled.
Prepare filling – Mash sugar, lemon zest, softened butter, and lemon juice to a spreadable paste.
Roll & fill – Punch down dough; roll to a 12 × 8 in rectangle. Spread filling, leaving ½ in border on one long edge.
Shape – Roll up tightly from the opposite edge; pinch seam. Slice log into 12 even pieces; set cut-side up in a greased 9 × 13 in pan.
Second rise – Cover and proof 30 min while heating oven to 350 °F / 175 °C.
Bake – Bake 25–30 min until golden and centre registers ~190 °F. Cool 10 min.
Glaze – Whisk powdered sugar, lemon juice, and melted butter until smooth. Drizzle over warm rolls; garnish with extra zest. Serve warm.