Every recipe that calls for a whole vanilla pod assumes you can open one cleanly. It takes thirty seconds and a paring knife, and doing it well means no caviar left behind on the board.
What you need
A cutting board, a small sharp knife, and a supple pod. If your pod has gone stiff, it will still split, but a flexible one is easier to work with and scrapes cleaner.
Step one: flatten
Lay the pod on the board and run the back of your knife along it once, pressing gently. This flattens the natural curl so the pod sits still under the blade.
Step two: anchor and split
Hold the pod down at one end with a fingertip. Set the knife tip just below your finger and draw the blade down the length of the pod in one motion. You can split through both walls or only the top wall; for infusions, splitting the top is enough to open it up.
Step three: scrape
Turn the knife over and use the back of the blade, not the edge. Hold one end of the split pod flat and scrape along each half from end to end. The seeds gather on the blade as a glossy black paste. That is the caviar, and one pod holds thousands of seeds.
Use both halves of the harvest
The seeds go wherever the recipe points: custard base, cake batter, whipped cream. The scraped husk goes into the pot alongside them whenever the recipe involves liquid, then comes out before serving. Husk and seeds together give a rounder flavor than seeds alone. When the husk has done its work, it still has a second life ahead of it.
A note on quantity
As a working rule, one pod flavors roughly a liter of dairy. Scale up for stronger flavor or longer infusions, and remember that a split pod gives up its flavor much faster than a whole one.
Grade A pods are the ones to practice on: supple, high in moisture, and made for exactly this.