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1
Discard 1 or 2 outer layers from lemongrass and trim root end.
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2
Mince lower inch of stalks for gremolata crumbs (3 to 4 tablespoons).
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3
Thinly slice enough from remaining lower end of stalk to measure 1/4 cup, then finely chop for butter sauce.
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4
Cut remainder of stalks, except reedy branches at top, into 1/2-inch slices, then puree with oil in a blender until smooth, 2 to 3 minutes.
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5
Force puree through a fine sieve into a bowl, pressing hard on solids, then discarding them.
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6
Blend 1/3 cup lemongrass oil with minced lemongrass (for gremolata), parsley, and zest in cleaned blender until parsley is minced, about 30 seconds.
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7
Transfer to a bowl and add panko and salt, stirring until crumbs are bright green, then spread gremolata crumbs in a shallow (1-inch-deep) baking pan.
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8
Peel apples and cut out as many pearl-size balls as possible using melon-ball cutter.
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9
(Alternatively, cut apples into 1/4-inch dice.)
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10
Drop balls as cut into a small shallow baking pan and toss first with lemon juice, then with oil.
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11
Preheat oven to 350F.
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12
Simmer chopped lemongrass, shallot, peppercorns, bay leaf, and wine in a 2-quart heavy saucepan over moderately low heat until reduced to about 1/2 cup, 10 to 15 minutes.
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13
Pour through fine sieve into a bowl, pressing on solids, then discarding them.
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14
Return wine to saucepan and stir in cream.
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15
Bring to a simmer over moderately low heat and whisk in butter, a few pieces at a time, adding new pieces before previous ones have completely melted.
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16
(Sauce must not get hot enough to liquefy; it should be the consistency of a thin hollandaise.)
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17
Remove from heat and whisk in salt and pepper.
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18
Keep warm, covered, off heat.
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19
Bake gremolata crumbs in upper third of oven, stirring occasionally, until crisp but still green (not golden), 8 to 10 minutes.
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20
Bake apples in lower third of oven until just heated through, about 5 minutes.
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21
Open trout like a book so that they lie flat, then pat dry and season both sides with salt and pepper.
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22
Heat 1 1/2 tablespoons lemongrass oil in each skillet over moderately high heat until hot but not smoking.
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23
Slide 2 butterflied trout, skin sides down, into each skillet (they will fit better if you alternate them head to tail; don't worry if edges of fish go up sides of skillet slightly).
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24
Reduce heat to moderate and cook until only a patch of pink flesh remains in center of each fillet, 7 to 12 minutes (fish will continue to cook from residual heat; do not turn over).
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25
Carefully lift 1 trout with a slotted spatula, then rest spatula (with fish) on paper towels and blot both sides of fish lightly.
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26
Transfer fish to a plate, placing it off-center.
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27
Repeat with remaining trout.
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28
Spoon about 1/4 cup gremolata crumbs on 1 side of each fish, letting excess spill onto plate.
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29
Gently fold other side of fish over crumbs and pour butter sauce around it.
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30
Scatter apple pearls on top and sprinkle dish with more gremolata crumbs.
