01 -
Whisk together the sour cream, heavy cream, lime juice, and salt in a small bowl. Cover and refrigerate for at least 30 minutes while you prepare everything else.
02 -
Preheat the oven to 400°F (200°C). Rub both sides of each corn tortilla with olive oil and a pinch of salt. Arrange in a single layer on a large baking sheet. Bake 4 minutes, flip, bake 4 more minutes, flip again, and bake a final 4 minutes until deep golden and crispy throughout.
03 -
Heat a large skillet over medium-high heat. Add the diced white onion and cook for 1 minute. Add the ground beef and break it into small, even pieces. Cook until no pink remains, about 6 to 8 minutes. Drain any excess fat.
04 -
Return the beef to medium heat. Add the chili powder, cumin, garlic powder, salt, black pepper, red pepper flakes if using, and the water. Stir well, bring to a simmer, cover, and cook for 10 minutes. Stir once halfway through. The liquid should mostly absorb.
05 -
Heat the refried beans in a small saucepan over low heat, stirring until warm and easy to spread. Add a small splash of water if they seem too thick to work with.
06 -
Spread a generous layer of warm refried beans on each crispy tostada shell. Add a scoop of seasoned beef, then shredded lettuce, diced tomato, diced red onion, and sliced avocado. Finish with crumbled queso fresco and a drizzle of crema. Serve immediately.