Make the pesto by adding all ingredients to a blender and blitzing to combine. Add the eight tablespoons of olive oil and check for consistency – it should be a pleasantly chunky sauce. If it is too thick, add the remaining oil and continue to blitz until smooth. Check for seasoning. Add to a screw top jar, cover with a layer of olive oil (about 1cm deep) and set aside until ready to use. (Leftover pesto will last for a few weeks in an airtight jar in the fridge.)

To make the onion jam place a medium saucepan over medium heat. Add the olive oil, wait until the oil takes on a shimmer, then reduce the heat to low and add the onions. Sweat until white, translucent and soft. Add the salt, sugar and a quarter cup of vinegar and continue cooking over low heat until a dark, jam-like consistency is achieved (about 15 to 20 minutes). Taste to check for a balance of tartness and sweetness and adjust the sugar and vinegar as needed. Transfer to an airtight container. (Like the pesto, the onion jam will last a few weeks in the fridge.)

To assemble the sandwiches place a slice of sourdough on a chopping board. Smear generously with the pesto. Add slices of mozzarella to cover, serrano ham, two basil leaves and semi-dried tomatoes. Spread another slice of bread with onion jam and sandwich together. Repeat with remaining bread and ingredients. Toast in a sandwich press until the mozzarella is melted and oozing – this is a great sign that all the ingredients have properly heated through. Remove and eat immediately.

More toastie and jaffle recipes

Find more of Katrina Meynink's recipes in the Good Food Favourite Recipes cookbook.