In a large, non-reactive saucepan, combine the pitted apricots, sugar, water, lemon juice, and cinnamon (if using).

Bring the mixture to a boil over medium-high heat, stirring occasionally to dissolve the sugar. Once boiling, reduce the heat to maintain a steady simmer.

Simmer uncovered for approximately 90 minutes to 2 hours, stirring every 10-15 minutes to prevent sticking. The apricots should break down completely, and the mixture will thicken significantly.

Test for readiness: The butter should coat the back of a spoon thickly. If you prefer a very smooth texture, carefully transfer the mixture to a blender or use an immersion blender to process until completely smooth. Be cautious, as hot liquids expand when blended.

Return the smooth apricot butter to the saucepan and simmer for an additional 5-10 minutes to ensure any excess moisture evaporates and it reaches the desired spreadable consistency.

Remove from heat. Pour the hot apricot butter into sterilized jars, leaving 1/4 inch headspace. Wipe rims clean and seal. For short-term storage, cool to room temperature and refrigerate. For long-term storage, process in a boiling water bath according to standard canning procedures.