Trim the tough bottom inch off each broccolini stalk and halve any stems thicker than a pencil lengthwise, so every piece chars at the same rate. Pat completely dry with a towel, wet stalks steam instead of blister.

Set a 30 cm / 12-inch cast-iron skillet over high heat for 2 to 3 minutes, until it's just starting to smoke.

Add 1.5 tbsp olive oil and half the broccolini in a single layer. Let it sit undisturbed for 3 minutes until deep black spots form on the undersides.

Toss and cook 2 more minutes, until the stalks are tender-crisp when pierced with a knife tip and most pieces show char on at least one side. Transfer to a plate.

Repeat with the remaining oil and broccolini, giving the pan a few seconds to reheat between batches.

Return all the broccolini to the skillet off the heat. Add the sliced garlic and chili flakes, and toss for 30 seconds using the residual heat, just until the garlic turns fragrant and pale gold.

Add the lemon zest, lemon juice, salt, and black pepper. Toss to coat.

Pile onto a platter and scatter with toasted almonds and shaved parmesan if using. Serve right away while the edges are still crackling.