Tip: Take the chill off refrigerated eggs by setting them in a bowl of warm water while you prepare the other ingredients.
Using a food processor, grind together the whole almonds and the granulated sugar (use the food processor's pulse feature to grind the almonds and sugar so you don't turn the mixture into nut butter).
Transfer to a medium bowl.
Beat in eggs, butter, milk, honey, vanilla and orange peel until smooth.
Sift the flour, baking powder and salt over the egg mixture and fold in until just combined (sift the flour, baking powder and salt over the cake batter to avoid overmixing; for a tender crumb, fold in sifted dry ingredients with a rubber spatula until just combined).
Transfer the batter to the prepared pan.
Scatter the sliced almonds on top.
Bake until a toothpick inserted in the center comes out clean, 45-50 minutes.
Transfer the cake to a rack to cool.
Sift confectioners' sugar over the top just before serving.