Rinse the lentils and add to a small sauce pan. Put garlic cloves, the half onion and the herbs in a sachet or cheesecloth and add to the pot. Cover lentils with a few inches of water, and add a small amount of salt, about ½ tsp.
100 g Black caviar lentils, ½ medium onion, 2 cloves garlic, 3 sprigs fresh herbs, ½ tsp salt
Turn heat to medium-high and bring to a gentle boil and then immediately turn down to a low simmer. Simmer for 25-30 minutes, until soft, checking at 15 minutes just in case. When lentils are cooked but still toothy, remove from heat immediately. If you are making them ahead, put the lentils in a storage container, let them cool briefly, and then place in the fridge.
Potatoes (best made just before mashing)
Rinse, peel and cut the potatoes into the same size chunks, about 1-inch. Place a steamer in the stovetop pressure cooker and add 1 cup water. Heat to full pressure and then turn off the burner and allow to set for 15 minutes. Release remaining pressure. Check for doneness; a fork should easily slide into the potatoes with no resistance, and the potatoes should almost, but not totally, fall apart. Steam longer if not done.
2 lbs Yukon gold potatoes
Remove the potatoes from the pressure cooker. Rinse out the pressure cooker and briefly dry it. Return it to the stove. Mash the potatoes over lowest heat, allowing steam to escape. They can be a bit chunky here still.
Preheat oven to 350ºF if you’re baking the dish right away; if not, hold off on pre-heating until you’re ready to bake. (The combined dish can be refrigerated for a bit before baking, if desired.)
Turn off the stove and add 60g butter, 80g cream cheese and about 2 tbsp milk (you may need more). Mix and mash everything together. You can take pauses to allow the butter and cream cheese to melt, if that's easier. Add a bit of salt and pepper.
60 g butter, 80 g cream cheese, 2 tbsp milk, ½ tsp salt, ½ tsp black pepper
Stir well and and set aside as you finish the lentils.
Finish lentils
Discard the herbs and other ingredients before continuing, if you haven't already. In a medium saucepan or high-sided skillet, melt 1 tbsp butter over medium heat. Add drained lentils along with just enough of their cooking liquid (less than ¼ cup) to moisten slightly. Bring to a simmer, then cook until lentils are heated through and enough liquid has evaporated that the lentils are coated in a creamy glaze but there isn't any standing liquid.
1 tbsp butter
Add the balsamic vinegar 1 tsp at a time until the lentils have a pleasant bright flavor (it should taste like a light contrasting tang, but not strongly sour). Season with salt and pepper.
1 tbsp balsamic vinegar
Combine and bake
Add the lentils to the mashed potatoes and stir to combine. Add to the baking dish. (You can briefly refrigerate here if needed.)
Bake at 350ºF for 5-15 minutes, until heated through.