Combine vinegar, sugar and water in a bowl for the pickled jalapeños.
Slice the jalapeños and place in a jar. Pour in the pickling brine and cover.
Pickle the jalapeños at least an hour before serving, preferably the day before. Store in the refrigerator.
Preheat the oven to 225°C.
Heat 3 tbsp butter in a skillet. Cook the panko bread crumbs over medium heat until golden. Add a pinch of salt. Set aside while preparing the macaroni.
Cook the macaroni according to the instructions on the package.
Finely chop the garlic and jalapeño. Cook in a saucepan in the remaining butter. Whisk in the flour. Add milk and cream, a little at a time, while constantly whisking. Cook until sauce thickens.
Let the sauce simmer for about 1 minute. Add vinegar, most of the cheese and salt.
Mix the sauce with the macaroni and pour into an oven-proof skillet or large baking dish.
Sprinkle with the remaining cheese and crispy panko bread crumbs
Bake on the center rack in the oven for 15 minutes.
Top with finely chopped parsley and pickled jalapeños. Serve immediately.