1. Melt 3 tbsp. of the butter in a medium pot over medium heat. Add onions and cook, stirring occasionally, until soft and translucent, 8-10 minutes. Add 9 tbsp. of the butter, the lentils, parsley, thyme, bay leaf, and allspice and stir until butter melts and lentils are well coated. Stir in stock and lemon juice. Bring to a boil over medium-high heat. Reduce heat to mediumlow and gently simmer haggis until lentils are soft but not mushy, about 45 minutes.