Place the olive oil in a small sauce pan over medium high heat.
Add the onion and garlic and cook for about 5 minutes, until the onions begin to soften. Stir frequently.
Add the lentils, vegetable stock, thyme, salt, and pepper.
Reduce the heat to a simmer and cook the lentils for about 20 to 25 minutes, until the lentils soften but still have a slightly firm texture.
Add additional vegetable stock 2 tablespoons at a time if the liquid evaporates before the lentils are cooked.
When the liquid has evaporated and the lentils are cooked, add the mustard and butter. Fold together until well blended.
Serve.
