Simmer chicory in water with lemon juice, sugar, salt, and peppercorns for 45 to 60 minutes.
Drain the chicory on a wire rack and press out excess moisture with a towel.
Preheat your oven to 190°C.
Boil 100ml of water with 10g butter, cook chard stalks for 20 minutes, then cook leaves for 3 minutes.
Melt 35g butter, whisk in 35g flour, then gradually whisk in 450ml milk until thickened.
Stir in 100g cheese and mustard until melted and season to taste.
Wrap each chicory in ham, place over chard in a dish, cover with sauce and 50g cheese.
Bake at the top of the oven for 25 minutes until golden brown.