Reheat & crisp the brisket (3–5 min)
Heat cast-iron over med-high. Add 1 Tbsp tallow or brisket fat.
Add chopped brisket in a single layer; don’t stir for 1–2 min to crisp edges.
Splash in 1–2 Tbsp beef broth or water if the meat looks dry; toss once.
Push brisket to one side; lower heat to medium.
Cook add-ons (3–6 min)
In the open side of the skillet, add a little fat if needed.
Sauté onion + jalapeño 2–3 min until fragrant; fold into brisket.
If using potatoes, crisp separately first or add par-cooked hash browns now; season with salt/pepper.
Soft-scramble the eggs (2–3 min)
Scoot mixture to the edges to make a well. Add ½ Tbsp fat if pan’s dry.
Pour in eggs and let set 10–15 sec, then slowly push from edges to center for soft curds.
When just set (still glossy), kill heat. Eggs will finish with residual heat.
Warm tortillas (while eggs finish)
On a preheated comal/skillet 30–45 sec/side until puffed spots appear.
Keep warm in a tortilla warmer or wrapped in a towel.
Build & serve
Fill tortillas with brisket-egg mix, sprinkle cheese, add beans/potatoes if using.
Top with salsa/pico, cilantro, and a squeeze of lime. Eat immediately.