Place 75 grams of the biscuits into a food processor and pulse until the consistency of course breadcrumbs. Tip into a bowl and set aside. Place the remaining 125 grams of biscuits and brown sugar into the food processor. Process just until the biscuits are finely ground. Add evaporated milk and process for about 1 minute.
Finally, add butter, lemon juice and cinnamon and process again for about 30 seconds. Tip into the bowl of biscuit crumbs and mix well.
Store the spread in a clean, airtight jar in the refrigerator for about a week.