Preheat the oven to 350° and spread the almonds out into an even layer on a baking sheet lined with parchment paper. When the oven is preheated, toast the almonds for 10-12 minutes, tossing them halfway through cooking time, until lightly browned. Remove from the oven and allow to cool.
While the almonds are cooling, mix together the sugar, melted butter, orange-flavored liqueur, rum, vanilla extract and orange zest in a large mixing bowl. Chop up the cooled toasted almonds finely and then mix them into the butter and sugar mixture. Add in the eggs and stir to combine.
In a separate mixing bowl, whisk together the flour, baking powder, and salt to remove any lumps.
Add the dry ingredients into the wet ingredients and stir until just combined into a thick and sticky dough.
Cover the mixing bowl with plastic wrap and refrigerate the dough for 30 minutes.
Line the baking sheet used to toast the almonds with a clean piece of parchment paper and turn out the chilled dough onto the prepared baking sheet.
With wet hands, form the dough into a large loaf shape that is approximately 8 inches wide by 13 inches long.
Bake the loaf in the oven for 20-25 minutes until it is golden brown. Remove it from the oven and allow it to cool for 15 minutes.
Transfer the slightly cooled loaf to a cutting board and using a serrated knife, slice it into 12 equal slices and then cut each slice in half for a total of 24 biscotti. Place the sliced biscotti directly onto two unlined sheet pans so they are cut side down.
Bake for an additional 15-20 minutes until they are golden brown and crispy. Remove them from the oven and let them cool completely on a cooling rack.
Once the biscotti are completely cooled, place the chocolate in a microwave-safe bowl. Microwave in 30-second increments at 50% power, stirring in between. Once the chocolate is 75% melted, stop heating it and stir it until it is completely melted.
Dip the biscotti ends into the melted chocolate and then transfer them to a sheet of parchment or wax paper to dry.