Line an 8×8-inch pan with waxed paper and dust with cornstarch.

In a medium saucepan, whisk together cornstarch, cream of tartar, and 2 cups of water over medium heat until smooth and thickened, about 8 minutes.

In a separate saucepan, combine sugar, gelatin package, and 1 cup water. Bring to a gentle boil, stirring until sugar and gelatin dissolve. Simmer for 3 minutes.

Gradually pour the hot sugar syrup into the thickened cornstarch mixture, whisking constantly. Reduce heat to medium-low and cook, stirring frequently, until the mixture is glossy and very thick, about 15 minutes.

Remove from heat and stir in orange zest, orange juice, and extract.

Pour mixture into the prepared pan, smooth the top, and sprinkle lightly with cornstarch. Let rest uncovered at room temperature for 8 hours or overnight.

Dust top with additional cornstarch, invert onto a cutting board, peel off paper, and cut into 1-inch squares. Dust cut sides to prevent sticking.