Preheat oven to 350 degrees F. Spray a 9x13’’ baking pan with olive oil and set aside.
Add bacon to a medium sauce pan or Dutch oven and place over medium heat. Cook until bacon is crispy and cooked through, about 11-15 minutes. Use a slotted spoon to remove bacon to a paper towel lined plate and set aside.
Pour off all but 2 tablespoons of bacon grease*(if necessary) and add the jalapenos, leeks, salt and pepper. Increase heat to medium high and sauté, stirring occasionally, until leeks have softened, about 4 minutes. Add garlic and cook until fragrant, about 1 minute. Add in the heavy cream and half-and-half. Bring to a simmer and immediately remove from heat. Add in both cheese (1 cup each) and stir until cheese is completely melted. Stir in bacon and parsley.
Using a large spoon, add just enough of the cheese sauce to the greased pan to barely cover the bottom. Add the potatoes to the pot with the remaining cheese sauce and gently toss to thoroughly coat. Use a slotted spoon to transfer the potatoes to the greased pan (using a slotted spoon will keep some of the cheese sauce in the pot). Top the potatoes with the remaining cheese sauce in the pot.
Cover the baking dish with aluminum foil and bake for 1 hour. Remove from oven and sprinkle with additional cheese (if using). Bake uncovered for 10 minutes. Use a small fork or toothpick to test potatoes for doneness. Switch oven to broil and cook until top is golden brown, about 1-2 minutes depending on the strength of your broiler.
Let stand 5 minutes before serving. Enjoy
*Jalapenos- For spicy potatoes – leave seeds intact in both jalapenos For medium - spicy potatoes completely seed one jalapeno and leave the seeds intact in the other. For mild - spicy potatoes – completely seed both jalapenos. *Cheeses- shred an additional ¼ Cup of each cheese for topping potatoes. Sprinkle the cheese evenly over potatoes after you remove the aluminum foil, then continue to bake as directed. *Bacon Grease – don’t simply discard bacon grease, pour it into a small container with a tight fitting lid and store it in your refrigerator. Use it in place of butter or oil to add bacon flavor to dishes. *To Make in Advance – Cook according to directions, covered, for one hour (do not sprinkle with extra cheese if using). Allow to cool on counter for 20 minutes. Covered the dish and transfer it to the refridgerator. When ready to serve, remove from fridge and set on counter for 30 minutes to remove chill. Preheat oven to 350 degrees F. Bake, covered for 20-25 minutes. Remove foil and continue baking as directed. *You can also make the potatoes in individual baking dishes. Bake according to the same directions above. *Recipe adapted from Flemings Site, but they recently removed their recipe from website.