Line a 9x13-inch pan with parchment or foil. Dust lightly with confectioners' sugar.
Combine granulated sugar, corn syrup, and water in a heavy 3-quart saucepan.
Warm over medium heat, stirring just until the sugar dissolves and the mixture looks clear.
Clip on a candy thermometer. Boil without stirring until the syrup reaches 300°F (hard-crack).
Remove from heat. Let bubbles settle for 10–15 seconds, then stir in cinnamon oil and food coloring. Ventilate; fumes are strong.
Immediately pour the hot candy into the prepared pan and tilt to spread evenly.
Cool completely until firm, about 30–45 minutes.
Dust the top with more confectioners' sugar. Lift out, crack into pieces, and toss to coat.
Store candy in an airtight container at room temperature.