Heat a large skillet over a medium flame.
Add half the butter and swirl it around until the surface is coated and all the butter is melted. Place two of the slices of bread in the pan and spin the bread in the melted butter to coat the bottom in butter.
Spread the tuna evenly over both pieces of bread in the pan.
Lay two slices of Gouda cheese on the tuna then the chopped sundried tomatoes and the other two pieces of bread. Press down on each sandwich. Once the bottom of the tuna melts has toasted, flip them, and add the rest of the butter.
Swirl to coat the bread in the butter and finish cooking until both sides are toasted.
Remove from the pan and cut into pieces and serve.
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