Line a rimmed baking sheet with a silicone baking mat or well-buttered foil. Measure all ingredients before heating. Keep children and pets away from the work area. Use a candy thermometer and a heavy saucepan with plenty of headroom.

Combine sugar, corn syrup and water in the saucepan. Heat over medium, stirring until the sugar dissolves. Once boiling, stop stirring and cook until the thermometer reads 300°F (149°C), hard-crack stage. Watch closely near the end; timing varies.

Remove from heat. Using a long-handled heatproof utensil, carefully stir in peanuts, butter and salt, then vanilla and baking soda. The mixture foams and remains dangerously hot. Do not touch or taste it.

Immediately pour onto the prepared sheet. Spread thinly with a lightly oiled heatproof spatula, without touching the candy. Leave undisturbed until completely cool and hard, about 45 minutes. Break into 24 approximate pieces.