Canola oil, for greasing
1 1⁄2 cups sugar
3⁄4 cup light corn syrup
1⁄4 cup honey
3 tbsp. unflavored powdered gelatin,
softened in 1⁄2 cup cold water
3⁄4 cup Dutch-process cocoa powder, sifted
2 tbsp. cornstarch
1. Grease an 8" x 8" baking pan, line bottom and sides with parchment paper, and grease paper. Grease a rubber spatula; set aside.
2. Combine sugar, syrup, honey, and 1⁄2 cup water in a 2-qt. saucepan over medium-high heat. Bring to a simmer; cook, without stirring, until syrup reaches 250° on a candy thermometer. Remove from heat; let cool to 220°.
3. Meanwhile, bring 1⁄2 cup water to a boil in a small saucepan. Place bowl of gelatin over boiling water; whisk until gelatin becomes liquid. Transfer to the bowl of a stand mixer fitted with a whisk; add 1⁄2 cup cocoa powder. Add cooled sugar syrup to gelatin; whisk on high speed until mixture holds stiff peaks, 5–6 minutes. Pour mixture into prepared pan; smooth top with oiled spatula; let cool until set, 5–6 hours.
4. Combine remaining cocoa powder and cornstarch in a bowl and transfer to a strainer; dust work surface with mixture. Slide a knife around edge of pan to release marshmallows; remove from pan. Dust cocoa mixture over top. Using a slicing knife dusted with cocoa mixture, cut marshmallows into forty 1 1⁄2" squares. Toss marshmallows with remaining cocoa mixture.