Toast the sesame seeds in a dry skillet over medium heat, stirring frequently, until golden and fragrant (about 2–3 minutes). Let cool slightly, then combine toasted sesame seeds with thyme, sumac, oregano, salt, and optional Aleppo pepper. Transfer to a shallow bowl or plate and set aside.

In the bowl of a stand mixer fitted with the dough hook, add water, milk, sugar, honey, and cooled melted butter. Add flour, salt, and instant yeast. Mix on low speed until combined but still shaggy, about 1 minute. Cover and rest 20 minutes to allow the flour to fully hydrate.

Knead on medium-low speed for 5–6 minutes, until smooth, elastic, and very sticky but cohesive. With greased hands, shape dough into a loose ball and place in a well-greased medium bowl. Cover with plastic wrap and let rise at room temperature 1 ½–2 hours, until puffy, jiggly, and about doubled in size.

Line a sheet tray with parchment paper. Turn out the dough and divide into 8 equal pieces (about 100 g each). Shape each piece into a ball by pinching ends together and rolling on a surface without flour to seal. Then gently press to flatten into rounds. Dip both sides of each round into the za’atar mixture, pressing down firmly so it adheres. Place coated rounds on the prepared tray, leaving space between them. Loosely cover with plastic wrap and let rise about 1 hour, until noticeably puffy.

Preheat oven to 350°F (175°C). Heat 2 Tbsp olive oil in a cast-iron skillet over medium-low heat for 2–3 minutes. Working in batches (3–4 at a time depending on pan size), cook muffins 4–5 minutes per side, until deep golden brown. Maintain medium-low heat to prevent the za’atar from burning. Transfer seared muffins to a parchment-lined baking sheet. Bake for 8–10 minutes, until the centers are fully cooked (internal temp ~200°F). Let cool 20–30 minutes before splitting. Split by piercing around the edge with a fork and pulling apart; this gives classic nooks and crannies.