Preheat the oven to 180°C (355°F). Grease and line a cake pan with baking paper.

Finely grate the zest from 2 lemons. Place the lemon zest and 220 g granulated sugar in a large mixing bowl.

Rub the lemon zest into the sugar with your fingertips. Continue until the sugar is fragrant and slightly damp.

Add 4 large eggs to the lemon sugar. Whisk until the mixture is smooth and slightly paler.

Add 250 ml double cream and 100 ml lemon juice. Whisk until fully combined.

Pour in 100 ml sunflower oil. Whisk until the batter is glossy and homogeneous.

Add 280 g all-purpose flour and 120 g ground hazelnuts. Fold gently until almost incorporated.

Add 14 g baking powder to the batter. Fold just until no dry streaks remain.

Pour the batter into the prepared cake pan. Smooth the surface with a spatula.

Bake the cake at 180°C (355°F) for 50 to 60 minutes. Check that a skewer inserted in the center comes out clean or with a few moist crumbs.

Combine 150 ml lemon juice for syrup and 70 g granulated sugar for syrup in a small saucepan. Heat over low heat until the sugar dissolves.

Simmer the lemon syrup gently for about 10 minutes. Remove the saucepan from the heat.

Remove the hot cake from the oven. Pierce the top all over with a skewer.

Slowly pour the warm lemon syrup over the hot cake. Leave the cake in the pan until it absorbs the syrup.

Let the syrup-soaked cake cool until warm. Transfer it to a cooling rack.

Combine 115 g icing sugar and 22 ml lemon juice for glaze in a bowl. Stir until a thick but pourable glaze forms.

Stir 1 tablespoon chia seeds into the lemon glaze. Spoon the glaze over the warm or fully cooled cake.

Let the glaze set before slicing. Serve the cake at room temperature.