Grilled Cheese on Sourdough with Apple Onion Relish

Who doesn't love grilled cheese? My favorite is using my homemade sourdough, two kinds of cheeses (just like with mac, something tangy + something melty seems to be best), along with my homemade apple-onion-ale preserves I've been making for over a decade. Best pieces of advice I got for making grilled cheese? 1) Butter on one side, mayo on the other (even if you hate mayo), and 2) Low and slow, which ensures everything melts inside while the bread doesn't burn. Hella yum.