Bake Tsoureki: make orange-scented braided loaves with mahlepi and mastiha for festive mornings.
Gently heat the whole milk with the unsalted butter and half of the granulated sugar in a small saucepan just until the butter melts and the sugar dissolves; you want a warm, slightly glossy mixture that will cool to lukewarm over about ten minutes. Take care not to scorch — the goal is a smooth, milky emulsion with a faint buttery sheen that will comfort the yeast later on.
Combine the lukewarm water with the remaining teaspoon of sugar and sprinkle the active dry yeast over the surface in a small bowl or measuring cup. Let it rest undisturbed until it becomes very foamy and fragrant, a living, aerated cloud that smells faintly bready — about five to ten minutes.
Whisk the cooled milk-butter mixture and room-temperature eggs into the foamy yeast. You should end up with a warm, pale-yellow liquid that looks slightly glossy from the butter and flecked with orange zest — calm, homogenous, and ready to meet the flour.
Add the flour, orange zest, mahlepi (or almond extract), salt, and mastiha to the wet mixture and mix with a dough hook on medium-low until a sticky, elastic dough forms — about six minutes. Listen and feel for the dough that clings to the bowl bottom but pulls away from the sides and makes a faint slapping sound; the surface should be smooth with a slight sheen and a tension that springs back when touched.
Turn the dough onto a lightly floured surface, form it into a smooth ball, and place it into a lightly oiled bowl, turning to coat. Cover and set in a warm, draft-free spot until doubled in size — roughly one to one and a half hours — until the dough feels pillowy and airy when gently pressed.
Punch down the risen dough, divide it in half, and work with one half at a time: cut it into three equal pieces, roll each into about 12-inch ropes with even taper, and braid them together, tucking the ends under so the braid stays neat. Repeat with the other half and place the two raw braided loaves on a parchment-lined, rimmed baking sheet; the braids should show smooth, slightly floured surfaces and clear strand definition.

Loosely cover the baking sheet and let the braided loaves rise in a warm place until noticeably puffed and almost doubled, about an hour. As they swell, they smooth into soft, plump braids with visible strand separation. Preheat the oven to 350°F while they finish proofing.
Whisk the remaining egg with a tablespoon of milk and gently brush the risen loaves to achieve a glossy, lacquered surface. Sprinkle the slivered almonds (or sesame seeds) evenly so they sit on the glaze and will toast to a delicate, crisp, nutty crown in the oven.
Bake the loaves for 20–25 minutes until puffed and a deep golden brown, the crust glossy and taut and the almonds toasted. Transfer the sheet to a wire rack so the loaves cool slightly; when sliced, the crumb should be tender, pale yellow, and slightly springy, laced with the aromatic lift of orange and mastic. Serve warm or at room temperature, store cooled in an airtight container for up to a week, or slice and freeze for longer storage.
