Preheat the oven to 350ºF and line a baking sheet with parchment paper.
Add the butter, sugar, baking powder, vanilla, orange zest and juice, and salt to a mixing bowl. Mix until smooth and creamy.
Add the eggs, one at a time, mixing well after each addition.
Carefully sift in the flour and dried Earl Grey tea, and mix again until a thick, sticky dough forms.
Divide the dough in half and place each piece on the prepared baking sheet. Carefully pat and shape each piece into a rectangle roughly 1/2 - 1 inch thick.
Bake for 22 minutes, until the top of each log is golden and dry. Remove from the oven and let cool for 20 minutes.
Once they're cooled, use a serrated knife to slice each piece into 1/2-inch wide cookies. Stand each cookie on its side on the baking sheet.
Bake again for 20-22 minutes, until the cookies are completely dried out and crispy.
Remove from the oven and let cool completely. Dip and decorate as desired.
Biscotti will keep in an airtight container at room temperature for several weeks.