Combine corn or peanut oil, sesame oil, scallions, ginger, Szechuan pepper, red chili pepper flakes, and kosher salt in a heavy, non-aluminum 1 1/2-quart saucepan.

Rest a deep-fry thermometer on the rim of the pot.

Over moderately low heat, bring the mixture to a bubbly 225 degrees F, stirring occasionally.

Simmer for 15 minutes, checking to ensure the temperature does not rise.

Remove from the heat and let stand until cool or overnight.

Strain the oil without pressing on the solids; then, discard the solids.

Store the oil in an impeccably clean glass jar at cool room temperature.