KITCHEN PRACTICE 3 — Splitting (and Correctly Mounting) a Butter Sauce
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Chapter: French Cookery 6 — Sautéing & Building a Pan Sauce

TASK
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Deliberately return a butter-mounted sauce to a boil and watch it
split, then make a fresh batch mounting the butter correctly, off
the heat, for comparison.

WHAT TO DO
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1. Deglaze a hot, empty pan with a splash of wine or stock, scraping
   up any fond, and reduce by roughly half.
2. Take the pan off the heat and whisk in a few cubes of cold
   butter, one at a time, until the sauce looks glossy and slightly
   thickened.
3. Deliberately break your own good habit: return the pan to direct
   heat and bring the sauce back up to a boil for a minute or so.
4. Watch what happens to the sauce's own texture and appearance as
   it boils.
5. Once you've seen it split, start a fresh small batch of deglazed,
   reduced liquid, and this time mount the butter in correctly — off
   the heat the entire time, never returning it to a boil — for
   direct comparison.

WHAT TO EXPECT
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- The reboiled sauce should visibly separate — the butter's fat
  pooling and separating out from the liquid, leaving a thin, greasy
  layer rather than the smooth, glossy sauce you had a moment before.
- The correctly-made second batch should stay smooth and glossy
  throughout, with no separation at all, since it never returns to
  direct heat once the butter goes in.
- If you taste both, the split sauce often tastes noticeably
  greasier and less cohesive on the tongue, even though the exact
  same ingredients went into it.

WHY THIS WORKS AS AN ANSWER
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Watching a mounted sauce split from reboiling makes the fragility
this chapter warns about directly visible, in a genuinely low-stakes
setting rather than mid-way through a real dinner. It's also the
same underlying lesson Chapter 5's hollandaise already taught in a
different form — a butter-based emulsion has a real, narrow window
of stability, and heat is consistently the thing that breaks it.