Melt 3 tablespoons of the butter in a skillet. Add finely minced garlic and cook on medium-high until translucent, 3-4 minutes.
Meanwhile, trim the connective tissue off of the liver and slice to thin strips. Add beef liver to pan, increase to high heat. Sprinkle with thyme, salt, and pepper. Sear liver for 60 seconds on each side.
Remove liver from heat and let cool, about 5 minutes. Transfer to a food processor or blender and puree until smooth. While blending/pureeing, add the remaining butter and cream (if using). Add more salt and pepper to taste, if desired.
Once the mixture is completely smooth, remove from blender and put in ramekins or a glass container and cover tightly. Chill in the fridge for at least 4 hours or overnight (preferred) to harden and let flavors meld.
Serve with cucumber, celery, bacon or just a spoon.