Very Fine chop shallots ( pref), 2nd pref red onion. Last choice normal onion. It is good to get some of the sweetness from the shallot / red onion.
Gentle Fry until soft. Fine grate Garlic towards the end of cooking. Be careful not to burn this.
Add whole peppercorns. Black or Green, mix any are fine.
Add stock, about 500ml. Stock cube is fine, be aware they have salt added so you may need to balance the flavour. Tradional is beef stock. Veg is fine if you pref.
Bring to boil reduce it down and starts to thicken.
Add cream – 100ml whipping cream.
Boil until nice and thick.