Slice the bacon and fry in a small/medium skillet over a medium-high heat until the fat is starting to render, stirring regularly, around 10 minutes.
Finely chop the onion and garlic, peel and finely dice the apple, and add all to the pan. Cook, stirring regularly until the onions have softened and gone translucent and the bacon is crisping, another roughly 10 minutes. If you have excess fat in the pan, drain it off - you want a little left but no more than around a tablespoon or two.
Add the cinnamon, water, brandy, sugar and molasses and stir in well. Once it boils, reduce to a simmer and allow to cook for around 20-30 minutes, stirring occasionally, until it is nicely sticky.
Remove the bacon-apple mixture from the pan, draining off any remaining excess fat as you do so, to a sealable jar or similar. Allow it to cool and store in the fridge until needed.