In a small bowl, whisk together 1/4 cup mayonnaise, 1 tsp maple syrup, 1/2 tsp Dijon mustard, 1/2 tsp fresh lemon juice and 1/4 tsp apple cider vinegar (if using). Season with 1/8 tsp salt and a pinch (about 1/16 tsp) of black pepper. Taste and adjust: add a few more drops of lemon or a touch more maple if you prefer sweeter. Chill while you prepare the rest of the sandwich so flavors meld.

Prepare Kale & Tomato

Remove tough stems from the kale and tear leaves into sandwich-sized pieces. Rinse and dry thoroughly.

Heat 1 tsp olive oil in a small skillet over medium heat. Add kale, sprinkle with a pinch (about 1/8 tsp) of the salt, and sauté 2–3 minutes until wilted but still bright green. Remove from heat and set aside. (You can skip sautéing and use raw kale if you prefer; massaging with a tiny drizzle of olive oil helps soften raw kale.)

Slice the tomato into two 1/4" (6 mm) thick slices. Lightly season both sides with a tiny pinch of salt and pepper.

Cook Eggs

Option A — Fried Eggs (runny yolk)

Melt 1/2 tbsp butter in a nonstick skillet over medium-low heat. Crack two eggs into the pan, spacing slightly apart. Sprinkle the eggs with the remaining salt (about 1/4 tsp distributed between both) and black pepper. Cook until the whites are set but yolks are still soft, 3–4 minutes. For slightly cooked yolks, baste with a spoonful of the pan butter or cover for 30–45 seconds.

Option B — Over-hard or Scrambled (for fully set yolks)

For over-hard: cook as above 2–3 minutes, then carefully flip each egg and cook 1–2 more minutes. For scrambled: whisk eggs lightly before cooking, add to the buttered skillet, stir gently until just set and still moist. Season to taste.

Toast Buns & Assemble

Split the pain au lait buns horizontally. Spread the optional 1/2 tbsp butter on cut sides. In a separate clean skillet over medium heat, toast the buns cut-side down until golden and slightly crisp, about 1–2 minutes. Remove to plate.

Spread a generous layer (about 1–1.5 tbsp) of the maple aioli on both the top and bottom buns.

On the bottom bun place the sautéed kale (about 1/2 cup), then a slice of cheddar. Immediately place the hot egg on top of the cheddar so the cheese softens; if using two eggs, stack as you prefer. Place the tomato slice on top of the egg, then the second slice of cheddar if you prefer cheese both below and above the egg (optional). Finish with the top bun.

If you want the cheddar extra melty, return the assembled open-faced sandwich (without top bun) to the skillet over low heat for 30–45 seconds, cover with a lid until cheese softens, then cap with the top bun.

Serve immediately with hot sauce or red pepper flakes to taste, and enjoy.