Preheat the oven to 350 degrees . Spread the almonds on a baking sheet, toast for 10 minutes and let cool.
Transfer 1/2 cup almonds and 1 tbsp. sugar to a food processor; mix until finely ground. Add the flour, baking powder and salt; pulse to mix.
Using an electric mixer, beat the eggs, vanilla and remaining 3/4 cup sugar on high until thick and fluffy, about 3 minutes. Add the flour mixture; mix on low until just blended. Stir in the whole almonds.
Grease a baking sheet. Transfer the dough to the sheet and shape into three 2 1/2-by-10-inch loaves; smooth the tops. Bake until golden, about 25 minutes. Transfer the cookie loaves to a cutting board. Slice crosswise 1/2 inch thick.
Lower the oven to 325 degrees . Return the slices to the baking sheet, standing them upright. Bake until golden and crisp, about 20 minutes. Let cool.
Place a sheet of parchment on the work surface. In a medium saucepan, bring 1 inch of water to a simmer. Transfer half of the chocolate to a heatproof bowl; place on top of the pan. Stir occasionally until the chocolate is melted and warm, about 3 minutes. Sprinkle in the remaining chocolate; remove from the heat. Let stand for 2 minutes, then stir gently until smooth. Dip the biscotti bottoms into the chocolate, smoothing with an offset spatula. Place the biscotti on one of their cut flat sides on the parchment to set, about 15 minutes.