In mixing bowl, with the help of a whisk (manual or electric) beat the four whole eggs with the sugar. Now gradually add the sieved flour, already "mixed" with the sieved baking powder, mixing all the ingredients together well. Lastly add the almonds and the wholegrain biscuit crumbs and mix again.
Grease a baking tray with the oil (or line with baking paper and grease) and sprinkle a little flour over the surface. Roll the dough into cylinders of 3-4 cm in diameter, roughly the length of the baking tray, and then lay them on it. Brush with the egg yolk beaten with a teaspoon of milk and one of sugar, and bake in a preheated oven, at 160 °C, for 40 minutes. Remove from the oven and allow the "sweet" rolls to cool. When they are lukewarm, use a sharp knife and slice them diagonally to form the classic Cantucci biscuit shape.
Arrange them once again on the baking tray and place in the oven, turned off but still hot, and allow them to "dry out" for a few minutes (5, 10 at the most, depending on the heat of the oven). This “little trick" makes the Cantucci biscuits dry and crunchy, but (there is always a but!) if you overdo it with the time and the heat, they will become too dark and dried-out.
Once removed from the oven for the second time, leave them to cool on a cake rack so that they are "aired" on all sides.
This is the original, classic recipe for Cantucci biscuits which, in Tuscany, have always been known as "biscuits from Prato", the town a few kilometres from Florence from which they originate. Nowadays many of the Cantucci biscuits you find are too soft and spongy, lacking in charm, refined and "enhanced" with chocolate chips, all kinds of candied or dried fruit and, worse still, artificial ingredients and flavourings.