Line a quarter sheet pan (9"x13") with parchment paper and coat with nonstick spray.
Pour 1/2 cup [4 oz] cold espresso into the bowl of a stand mixer fitted with the whisk attachment. Sprinkle gelatin and cardamom over the espresso. Let the gelatin soften, about 15 minutes.
Clip a candy thermometer to the side of a 3 to 4 quart saucepan. Over medium-high heat, bring the sugar, corn syrup, salt, and an additional 1/2 cup [4 oz] cold espresso to a boil in the saucepan. Continue to boil without stirring until the syrup reaches 240°F, about 6 to 8 minutes.
Turn the mixer on low speed. Once the syrup reaches 240°F, quickly pour the syrup down the side of the bowl with the motor running. Increase the speed to high and whisk until the mixture becomes very thick and lukewarm, approximately 10 minutes.
Working quickly, scrape the marshmallow mixture into the greased pan. Smooth the top with a wet spatula and let stand uncovered until firm, about 4 hours.
Prepare a small bowl filled with powdered sugar. Turn the firmed-up marshmallow slab onto a work surface dusted with powdered sugar and remove the parchment paper. Using kitchen shears or a large sharp knife sprayed with nonstick spray, cut the marshmallows into eight 1-inch strips. Cut each strip into 12 1-inch squares. Coat each square in powdered sugar shaking off the excess.
Store in an airtight container up to 3 weeks.