Does Weapon Mastery allow the use of two one handed weapons e,g, over riding the restriction of only atacking with one weapon.

Or can you use 2 x one handed weapons in the same attack

or is the card badly worded

"Each time you perform an attack with either 1 Melee weapon with 2 hand icons or 2 Melee weapons with 1 hand icon each, you may exhaust this card to add 1 Surge to the results."

It doesn't change how you attack, it can grant you a surge if you meet the requirements.  If you have two melee weapons equipped, you still need to choose one for a given attack.

Triu said:

So its badly worded or "Each time you perform an …" (which is singular) "…….2 Melee weapons with 1 hand icon each,……." 

This suggest you can attack once with a two handed melee  weapon or use 2 one handed melee weapons in a single attack.

The golden rule is that cards override the rules and this is weapon mastery.

Found this on BGG , explains all : - 

1. At the start of the turn you choose which weapons you have equipped for that turn. 

2. You can only add one surge to the combat result (from weapon mastery) if you have one 2-handed melee weapon or two 1-handed melee weapons equipped.

3. You can only choose 1 weapon to attack with. Thus in the two cases above, you can attack with the 2-handed weapon or one of the 1-handed weapons.

Example:

A Berserker got the following weapons in his backpack:

2-hand sword
1-hand dagger
1-hand mace
1-hand shield

At the start of his turn he can equip:

Sword (He will get the bonus of weapon mastery)
Dagger and Mace (He will get the bonus of weapon mastery)
Dagger and Shield or Mace and Shield (He will not get the bonus of weapon mastery)

There is no equip phase after you've taken your actions, so if you have not chosen to equip a shield at the start of your turn you cannot switch to it after your attacks.