Spray a 13x9-inch glass baking dish with oil. Line with parchment, allowing a 2-inch overhang on the long sides. Spray parchment with oil; set aside.
Put granulated sugar, corn syrup, salt, and 3⁄4 cup water into a medium saucepan. Bring to a boil over high heat, stirring to dissolve sugar. Cook, without stirring, until mixture registers 238°F on a candy thermometer, about 9 minutes.
Meanwhile, put 3⁄4 cup cold water into the bowl of an electric mixer; sprinkle with gelatin. Let soften 5 minutes.
Attach bowl with gelatin to mixer fitted with the whisk attachment. With the mixer on low speed, beat hot syrup into gelatin mixture. Gradually raise the speed to high; beat until mixture is very stiff, about 12 minutes. Beat in Raspberry Chipotle Spice Rub and vanilla. Pour into prepared dish, and smooth with an offset spatula. Set aside, uncovered, until firm, about 3 hours, or overnight.
Sift 1 cup confectioners’ sugar onto a work surface. Unmold marshmallow onto confectioners’ sugar; remove parchment. Lightly brush a sharp knife with oil, then cut marshmallow into 2-inch squares. Sift remaining 1⁄2 cup confectioners’ sugar into a small bowl, and roll each marshmallow in the sugar to coat. Store in an airtight container for up to 2 weeks.