Add apples, butter, bay leaf, and water to a medium pot.
Bring to a gentle simmer over medium heat, then reduce to low. You're looking for a bare simmer: small bubbles breaking the surface, not a rolling boil.
Cover and cook for 30–40 minutes, stirring occasionally, until apples are very soft and falling apart.
Blend
Remove and discard the bay leaf.
Use an immersion blender to puree until smooth. (If using a regular blender, let the mixture cool slightly before blending.)
Serve
Serve warm or chilled. Try it with pork chops, yogurt, or just straight by the spoon.
Notes
Storage: cool completely and store in an airtight container in the fridge for up to a week, or freeze for up to 3 months. Serve warm or straight from the fridge, either works.