Preheat – Heat oven to 400°F with a sheet pan inside. Fold each parchment sheet in half, then reopen.

Make the Butter – Mix butter, capers, parsley, garlic, and lemon zest until combined.

Prep the Potatoes – Thinly slice potatoes (a mandolin is great here). You’ll want 9–12 slices per packet. Optional but worth it: place potatoes in a microwave-safe bowl with 2 Tbsp water, cover loosely, and microwave 4–5 minutes until just starting to soften. Drain well.

Build the Packets – On one side of each parchment sheet, layer potatoes in a slight overlap. Spray/drizzle with olive oil; season with salt + pepper. Top with shallots and spinach - season again with a little sprinkle of salt + pepper. Add 1 salmon fillet per packet and season generously with salt + pepper. Top with dollops of lemon caper butter and lemon slices.

Seal – Fold the empty half of parchment over the filling to meet the other side. Starting at one corner, make small overlapping folds all the way around the open edges, crimping tightly as you go to create a sealed half-moon packet. Twist or tuck the final corner underneath. It doesn’t have to look perfect, just try and make a good seal.

Bake – Place packets on the hot sheet pan. Bake 18–22 minutes, until salmon is cooked through and potatoes are tender. Open carefully, as the packets will release hot steam. Serve immediately and enjoy.