In a small saucepan over medium heat, heat 3/4 cup syrup just until it simmers. Reduce heat to low. Stir a small amount of hot syrup into egg yolks; return all to the pan, stirring constantly. Cook and stir until mixture is thickened and reaches 160°. Transfer to a large bowl; set bowl in ice water and stir for 2 minutes. Cool to room temperature.
In a large bowl, beat cream until stiff peaks form. Gently fold into the syrup mixture. Spoon into dessert dishes. Chill for at least 2 hours. Just before serving, drizzle with remaining syrup and sprinkle with hazelnuts.