Whisk the warm milk, sugar, and yeast in a small bowl and let sit 5–7 minutes until foamy. In a large bowl or the bowl of a stand mixer, combine the flour and salt. Add the yeast mixture, beaten egg, and melted butter. Stir with a wooden spoon until a shaggy dough forms.

Knead

If using a stand mixer, attach the dough hook and knead on medium-low for 6–8 minutes until the dough is smooth, elastic, and slightly tacky. If kneading by hand, turn dough onto a lightly floured surface and knead 8–10 minutes, adding small dustings of flour only if dough is excessively sticky.

First rise

Lightly oil a clean bowl, place the dough inside, turning to coat. Cover with plastic wrap or a damp towel and let rise in a warm draft-free spot until doubled, about 60–75 minutes.

Filling & Assembly

Prepare filling

While dough rises, mix the softened butter, brown sugar, and cinnamon in a bowl until evenly combined and spreadable. Stir in the chopped nuts if using.

Roll and spread

When the dough has doubled, punch it down and turn onto a lightly floured surface. Roll into a 12x18-inch rectangle about 1/4 inch thick. Spread the cinnamon-brown sugar mixture evenly over the dough, leaving a 1/2-inch border on one long edge.

Shape

Starting from the opposite long edge, tightly roll the dough into a log. Pinch seam to seal. Using a sharp knife or dental floss, cut the log into 12 equal pieces (about 1–1¼ inch each).

Second rise

Place the pieces cut-side up in a lightly greased 9x13-inch baking pan, leaving small gaps for expansion. Cover loosely and let rise until puffy and nearly doubled, about 30–40 minutes.

Bake & Finish

Bake

Preheat the oven to 350°F (175°C). Bake the rolls on the middle rack for 20–25 minutes, or until golden brown on top and cooked through (internal temperature ~190°F / 88°C). If the tops brown too quickly, tent loosely with foil for the last 5–10 minutes.

Prepare glaze

While rolls bake, whisk the powdered sugar with vanilla and milk until smooth and pourable. Add a few drops more milk if needed; it should be thick but able to drizzle.

Glaze and serve

Remove rolls from oven and let cool in the pan 8–10 minutes. Drizzle the vanilla glaze over the warm rolls and sprinkle with flaky sea salt. Serve warm. Store any leftovers tightly covered at room temperature for up to 2 days or refrigerate up to 5 days; reheat briefly before serving.