In a large bowl, use a hand mixer or stand mixer to cream the softened butter, sugar, and orange zest together until light and fluffy.
Beat in the eggs one at a time, mixing well after each addition.
In a separate bowl, whisk together 2 cups (240g / 8.5 oz) of the flour, the baking powder, and a pinch of salt. Gradually add this dry mixture to the wet , mixing on low speed until just combined and a smooth dough forms.
Lightly flour a clean work surface with the remaining ½ cup (60g / 2.12 oz) of flour.
Turn the dough out and knead gently for a few minutes, incorporating the flour until the dough is smooth and no longer sticky.
Divide the dough into pieces about the size of a large walnut (this should yield 24-30 pieces).
Roll each piece into a smooth ball, then place on a lightly greased or parchment-lined baking sheet. Use a spatula or the palm of your hand to gently flatten each ball to about ¾-inch thickness.
Arrange the flattened dough discs about 1 inch apart.
Bake in a preheated 400°F (200°C) oven for 10 minutes, or until they are slightly puffed and just beginning to turn golden at the edges.
Remove the baking sheets from the oven and let the rusks cool for a few minutes, just until they are cool enough to handle.
Using a sharp, serrated knife, carefully slice each warm rusk in half horizontally, like an English muffin.
Place the rusk halves cut-side up back on the baking sheets.
Reduce the oven temperature to 350°F (175°C).
Bake for another 8-10 minutes, or until they are completely dry, crisp, and a beautiful golden color.
Let them cool completely on a wire rack before storing in an airtight container.
