First put the blackberries in a pot with sugar and some water and cook until it reaches a syrup consistency.
In parallel, cut the onion and garlic into irregular shapes and put in a pan with butter.
Once the onion is al dente, add the peas, wait until warm, and then remove from the stove.
Put the peas in a blender, blend until smooth, taste, add salt if necessary, and set aside.
Apart from that, separate the syrup with the whole blackberries.
Put the tuna into the syrup and blend the blackberries until they reach a sauce consistency.
After marinating the tuna in syrup for a couple of minutes, coat with sesame seeds and slice.
For the assembly, first pour the mashed peas.
Lay the tuna over the mashed peas and finally add sauce.
