Position rack in center of oven and preheat to 350°F and line baking sheet with parchment paper.
Sift flour, baking powder and salt into medium bowl.
Mix sugar, melted butter, 3 eggs, vanilla extract, orange liqueur and zest in large bowl. Add flour mixture to egg mixture and stir with spatula until well blended. Mix in almonds.
Divide dough in half. Using floured hands, shape each dough half into 13 1/2-inch-long, 2 1/2-inch-wide log. Wrap in plastic wrap and refrigerate for at least 30 minutes.
Transfer both logs to prepared baking sheet, spacing apart. (They spread.)
Whisk egg white in small bowl until foamy; brush over top and sides of each dough log.
Bake logs until golden brown (logs will spread), about 30 minutes. Cool logs completely on sheet on rack, about 25 minutes. Maintain oven temperature.
*This is where I need to fix my quirks-I think I made my logs a little too thick, causing the middle to not cook as evenly as needed. I cooked mine for an extra 10-15 minutes. Next time I will not make them as "thick".
Transfer logs to work surface and discard parchment paper. Using a serrated knife, cut logs on a diagonal into 1/2-inch-wide slices. (I'll practice more next time!) Arrange slices, cut side down, on same baking sheet.
Bake for 12 minutes.
Turn biscotti over and bake until just beginning to color, about 8 minutes. Transfer to rack and cool.