Method:

Preheat oven to 350° F / 175° C. Line a half-sheet rimmed baking tray with parchment.

In a mixing bowl, whisk together flour, sugar, baking powder, and kosher salt.

Add cubed butter to flour mixture and use your hands to combine. The mixture will resemble breadcrumbs.

Add eggs, vanilla, and pistachio flavoring to the flour-butter mixture.

Use a bench scraper to bring the mixture together.

Add the white chocolate chips and pistachios, then use your hands to knead gently until a soft dough forms.

On a lightly floured countertop, divide the biscotti dough into two equal portions.

Roll each portion into a log, measuring approximately 7 inches long and about 1 1/2 inches wide.

Place two logs on prepared tray, making sure to allow a good amount of space between the two.

Use a pastry brush to the tops of the logs with beaten egg white.

Bake in preheated oven for 25 minutes. Remove from oven and cool for 10 minutes on tray.

Transfer logs to a cutting board.

With a gentle sawing motion, use a serrated knife to cut each log on the diagonal, creating 3/4-inch wide slices.

Place the slices upright on the parchment-lined tray and bake for an additional 15-17 minutes, or until dry and lightly golden on top.

Transfer pistachio biscotti to a wire rack and allow cool completely.

Once cool, melt the white chocolate in the microwave in short intervals, stirring frequently to prevent burning.

Stir in neon green gel food coloring, if using.

Transfer melted chocolate to a piping bag. Pipe in zigzags over the biscotti.

Sprinkle with crushed pistachios and white nonpareils.

Allow biscotti to sit at room temperature, uncovered, until white chocolate has set. Serve immediately.

Store leftover biscotti in an airtight container, layered between sheets of parchment, for up to three days. Leftover biscotti can also be frozen, and will thaw very quickly at room temperature.