Dust a little cornstarch over a worksurface to prevent sticking. Roll out white fondant and cut out letters to spell out 'on Wednesday we wear pink' using metal letter cutters. Transfer letters to a parchment-lined sheet pan and set aside.
In a bowl, mix ½ cup frosting with a few drops of deep pink gel food coloring with a spatula so that you get a hot pink color. Transfer to a piping bag. Set aside.
In a bowl, mix remaining frosting with one or two drops of soft pink gel food coloring with a spatula so that you get a pale pink color. Transfer to a piping bag. Set aside.
Mix nonpareils together and set aside.
Preheat oven to 375°F Line two baking sheets with parchment paper. Unroll one tube of dough on onto each prepared baking sheet. Set aside in the refrigerator.
Add chocolate chips, espresso powder, and salt to a bowl.
Add heavy cream to a small saucepan and heat over medium heat until just beginning to form small bubble around the edges. The cream should be hot, but not boiling. Pour the cream over the chocolate and let sit for 2-3 minutes.
Add in the butter and whisk until smooth, then let sit for 1-2 minutes.
Spread the chocolate ganache onto one of the dough sheets using an offset spatula, leaving a 2 inch border. Dollop the marshmallow fluff on top of the chocolate.
Pick up the second portion of dough along with the parchment and place over the filling, parchment side up. Peel off parchment.
Use a pizza cutter to trim away just enough dough to create clean straight edge on all sides.
Dip a fork in bench flour to prevent sticking and crimp the edges with a fork. Brush with egg wash. Bake for 15 minutes, rotating the pan halfway through. Let cool on the pan for 5-10 minutes.
Transfer the strudel to a serving platter or large cutting board. Pipe the light pink frosting over the entire strudel, leaving a small border. Spread with a small offset until smooth and covered. Sprinkle over nonpareils. Pipe on a squiggle design with the hot pink frosting. Position the fondant letters on top to read, 'on Wednesdays we wear pink.'.