1. Combine pumpkin purée, honey, brown sugar, pumpkin pie spice, cinnamon, vanilla extract, and salt in slow cooker and stir until evenly blended.

2. Cook on low for 2 1/2 to 3 hours, stirring every 30 to 45 minutes, until mixture darkens and thickens.

3. Check consistency by drawing a spoon through the center; if it leaves a line that does not fill back in, proceed, otherwise cook up to 30 minutes longer.

4. Transfer mixture to a mixing bowl and let cool for 15 to 20 minutes.

5. Add softened butter and additional honey to the cooled mixture.

6. Use electric mixer to whip on medium-high speed for 2 to 3 minutes until light and fluffy, scraping down the sides as needed.

7. Taste and adjust seasoning with more cinnamon or honey if desired.

8. Spoon the whipped butter into glass jars and refrigerate for up to two weeks or freeze for up to three months.