Rinse the lentils and place in a medium pot and cover with 5 cups water.
Add the onion and bay leaves.
Bring to a boil, reduce heat to maintain a simmer and cook until lentils are tender, about 20 minutes.
Stir in salt and set aside to cool.
While lentils cool, melt butter in a medium frying pan over medium heat.
Add shallots and cook, stirring frequently, until shallots start to caramelize, about 30 minutes.
Remove from heat, add the Tawny and stir, scraping any brown bits from the bottom of the pan.
Return to the heat and cook until all the liquid is gone.
Drain the lentils.
Pick out and discard the onion and bay leaves.
In a food processor, pulse the lentils, shallots and black pepper into a pate-like puree.
Add more salt and pepper, to taste.
Transfer mixture to a bowl or small baking dish for serving.
Cover and chill at least 4 hours, and up to overnight, allowing the flavors to mellow and blend.
Bring to room temperature before serving.