Step 1

Lightly butter a 13x9" baking dish, then line with parchment paper, leaving a 2" overhang on long sides. Lightly butter parchment. Cook 3/4 cup butter in a large pot over medium heat, swirling, until butter foams, then browns (be careful not to let it burn), 5–7 minutes. Add marshmallows and salt. Reduce heat to low and cook, stirring constantly, until marshmallows are melted and mixture is smooth, about 3 minutes. Add Nutella and stir until completely incorporated into marshmallow mixture, about 2 minutes.

Step 2

Remove pot from heat and add half of puffed rice to marshmallow mixture; stir with a nonflexible heatproof spatula or wooden spoon, scraping bottom of pot and folding, until cereal is coated. Add remaining cereal and fold until mixture is homogenous. (It’s a lot of cereal, so you’ll need to exert some effort.) If mixture is too stiff, heat over low while continuing to fold in cereal. Scrape into prepared pan; let cool slightly, then cover with a sheet of parchment paper. Press down firmly to make an even, compact layer (you want the top to be as flat as possible; a smaller pan, like a loaf or an 8x8" pan, works great for this). Cover crispies loosely with plastic and let sit until cool, about 2 hours.

Step 3

Just before serving, using parchment paper overhang, lift crispies out of pan and place upside down on a cutting board; remove parchment. Using a serrated knife, trim about 1/2" from all sides to make a squared-off rectangle, then cut into a 6x4 grid to make 24 squares. Place crispies on a wire rack, spacing at least 1" apart.

Step 4

To make half the crispies red, if desired, pulse freeze-dried strawberries in a food processor until finely ground; add luster dust and pulse just to combine. Using a fine-mesh sieve, dust 12 squares with strawberry powder, then, using a dry, clean sieve, dust remaining 12 squares with powdered sugar. Or feel free to dust all 24 squares with powdered sugar instead.

Step 5

Crispies can be made 1 day ahead. Leave in pan. Store tightly wrapped at room temperature. Cut into squares and coat just before serving.