Spread 1/2 tbs butter evenly on one side of each sourdough slice. Heat a skillet over medium heat. Place bread butter-side-down in the skillet and toast until golden and crisp, about 2–3 minutes. Flip briefly (30 seconds) to warm the other side, then remove and set aside on a plate.

Sauce

Make sriracha mayo by whisking together 2 tbs mayonnaise, 1 tsp sriracha, 1/2 tsp lime juice, and 1/8 tsp salt in a small bowl until smooth. Taste and adjust heat or acidity as desired. Set aside.

Egg & Cheese

Fry the egg

Heat 1 tsp neutral oil in a nonstick skillet over medium heat until shimmering. Crack the egg into a small bowl, then gently slide it into the skillet. Sprinkle 1/4 tsp salt and 1/8–1/4 tsp black pepper over the egg. For a runny yolk, cook until whites are set and edges are lightly crisp, about 2–3 minutes. For firmer yolk, cover the pan and cook an additional 30–60 seconds. Remove from pan and keep warm.

Melt cheese

Return the toasted sourdough (toasted-side up) to the skillet over low heat. Place shredded cheddar (1 oz) on one slice and cover the skillet with a lid for about 30–45 seconds until cheese melts. Remove from heat.

Produce & Toppings

Lightly season the tomato slices with a pinch of salt. Toss the arugula with a very light pinch of salt if desired. Chop or mince the canned chipotles if not already diced; measure 1 tsp.

Assembly

Spread about half of the sriracha mayo (roughly 1 tbs) on the non-cheese slice of toasted sourdough. On the cheese-topped slice, place the tomato slices evenly over the melted cheddar. Add the fried egg on top of the tomato.

Scatter the arugula over the egg, then sprinkle the diced chipotles evenly (1 tsp) across the greens and egg. If you reserved extra sriracha mayo, drizzle or spread the remainder on the top slice, then close the sandwich with the mayo-coated slice on top.

Press gently, slice in half if desired, and serve immediately while the egg yolk is still runny and cheese warm. Enjoy.