Mackerel Pressed Sushi (Saba Oshizushi)

Bahan-bahan (2 porsi)

• 1½ cups uncooked Japanese short-grain white rice
• 1 frozen marinated mackerel fillet (shime saba) ((defrosted in the refrigerator overnight))
• 6 shiso leaves
• 4 Tbsp seasoned rice vinegar (sushi vinegar) ((I used Kikkoman® Seasoned Rice Vinegar; or make my homemade sushi vinegar below))
• 4 Tbsp rice vinegar (unseasoned)
• 2 Tbsp sugar
• 1 tsp Diamond Crystal kosher salt