1. Preheat your oven to 425°F (220°C).

2. Heat butter in a large skillet over medium heat and brown the ground beef until it's cooked through.

3. Add taco seasoning mix and water to the skillet, and cook until the liquid is almost completely absorbed, then set the mixture aside.

4. Dice the tomatoes, setting some aside for garnish later. Remove the seeds from the yellow bell pepper and dice it as well.

5. Grease an oven-safe mold with butter or cooking spray. Create a layered gratin in the mold by alternating between the cooked ground beef, tortilla chips, diced tomatoes, diced bell pepper, crème fraiche (or substitute with sour cream), and taco sauce.

6. Finish the gratin with a layer of tortilla chips on top, then sprinkle shredded cheese evenly over the chips.

7. Bake the gratin in the middle of the preheated oven for approximately 10 minutes, or until the cheese is melted and bubbly.

8. Remove the gratin from the oven and garnish with diced avocado, the reserved tomatoes, and corn kernels.