Preheat oven to 350° F (175° C). Line 2 half sheet rimmed baking trays with silicone baking mats.

In a large mixing bowl, whisk all purpose flour, granulated sugar, baking powder, and fine sea salt.

Add the cubed butter use your hands to combine, rubbing between your fingertips until the mixture resembles breadcrumbs.

With a bench scraper, work in the eggs and vanilla extract, followed by the rainbow nonpareils and chocolate chips.

Finish kneading by hand until a soft dough forms.

On a floured work surface, divide the dough into 2 equal portions. Roll each portion into a log, approximately 7 inches long and 2 inches wide.

Arrange logs on prepared tray, allowing 4-5 inches in between the logs.

With a pastry brush, brush the tops of the logs with egg white.

Sprinkle with rainbow nonpareils, covering the entire surface of the log. With your fingertips, gently pat the sprinkles into the dough.

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

With a serrated knife, cut each log on the diagonal, creating 1-inch wide slices.

Arrange slices upright on trays, dividing equally between the two. Bake 15-20 minutes more, or until dry.

Transfer to a wire rack to cool completely.

Chocolate chip rainbow biscotti are best enjoyed within 1-2 days of baking. Store leftovers in an airtight container at room temperature for up to 5 days, or freeze for up to 3 months.