Melt 30 g butter over medium heat. Stir in 20 g flour and cook for 1-2 minutes. Gradually pour in 125 ml chicken broth while stirring, then add 125 ml cream. Simmer over medium heat for 10 minutes, stirring occasionally. Stir in the mixed herbs and season with salt, pepper, and sugar. Add 1 tablespoon lemon juice.
Preheat oven to 200°C (400°F). Season 6 chicken breast fillets with salt and pepper and place them in a baking dish. Pour the herb sauce over the fillets and sprinkle 40 g freshly grated parmesan on top.
Bake for 30 minutes until the chicken reaches 74°C (165°F) internally.