Make the syrup first: combine Granulated Sugar and Water in a saucepan and bring to a gentle boil, then reduce heat and simmer for about 8–10 minutes until slightly thickened; stir in Lemon Juice, simmer 1 more minute, then remove from heat and set aside to keep warm.
In a large bowl, cream together the Unsalted Butter and Powdered Sugar until light and fluffy.
Beat in the Egg, then the Egg Yolk and Vanilla Sugar until fully incorporated.
Fold in the Semolina, All-Purpose Flour, Baking Powder and a pinch of Salt to form a soft, slightly sticky dough; avoid overworking—if it feels very wet, rest 15–30 minutes to allow the semolina to absorb moisture.
Preheat the oven to 180°C (350°F). Shape the dough into small oval or round pieces (about walnut-sized) and place them on a baking sheet lined with parchment, spacing them a couple of centimeters apart.
Press each piece lightly with your thumb to make a shallow indentation and top with a Hazelnut. If you like a glossy finish, brush lightly with a little of the reserved Egg Yolk before baking.
Bake for 20–25 minutes, or until the cookies are evenly golden on top.
As soon as the cookies come out of the oven, pour the warm syrup evenly over the hot pastries so they can absorb it (hot cookies + warm syrup gives the best soak). Let them sit at least 30 minutes to absorb the syrup before serving.
Serve at room temperature; store any leftovers in an airtight container so they stay moist and fragrant.
