Preheat the oven to 180°C/160°C convection/gas mark 2-3 (approximately 350°F/325°F convection). Slice the almonds in half lengthwise and place on a baking sheet lined with parchment paper. Toast the almonds in the oven for 10-15 minutes, until golden brown. Separate the eggs. Beat the egg whites until soft peaks form, then gradually add 100 grams (approximately 1/2 cup) of sugar and continue beating until stiff and glossy. Beat the egg yolks with the salt, 1 tablespoon of hot water and the remaining sugar until light and frothy. Stir in the almond extract, speculoos and orange zest.
Fold the beaten egg whites into the egg yolk mixture, then stir in the flour, baking powder and toasted almonds and mix until a smooth dough is formed. Roll the dough out onto a floured surface into a long rectangle about 2 cm (approximately 3/4 inch) wide. Place on a baking sheet lined with parchment paper and bake for 35 minutes. Remove from the oven, allow to cool slightly, then slice diagonally into 1 cm (approximately 3/8 inch) thick strips. Cool completely on a wire rack and store the biscotti in an airtight container or wrap in cellophane for gift giving.