Begin with crema. Ideally you make this a few hours to a day prior. Whisk together 1/2 cup sour cream, 1/2 cup heavy cream, 1/2 teaspoon salt and 1 Tablespoon lime juice. Cover and place in fridge to store before serving.
Heat oven to 400 degrees.
Spread out the corn tortillas on a large baking sheet and drizzle with olive oil and a pinch of salt. Rub the olive oil all over the tortillas on each side.
Bake in 4 minute increments flipping between each. Bake until the tortillas are crispy and a golden brown color. This should take 2 flips or 12 minutes.
SPICY GROUND BEEF:
Heat a nonstick skillet on the stove top on a medium-high heat. Drizzle the pan with olive and drop in the diced white onion. Let cook 1 minute and then add the ground beef. Break up the ground beef into equal pieces until browned.
Drain the meat if needed. If using a really lean meat, you may not need to. Put the meat back in the pan and add 1/2 cup water and the seasonings. Red pepper flakes are optional if you just want a little extra kick. Bring to a simmer, lower heat and cover for 15 minutes. Stir a few times to ensure the meat isn’t sticking.
GROUND BEEF TOSTADAS:
Heat up the refried beans as the meat finishes cooking and assemble your tostadas.
Start with a layer of refried beans on the crispy corn tortilla, add some spicy ground beef, top with shredded lettuce, diced red onion, diced tomato, and sliced avocado. Sprinkle with queso fresco and then drizzle with the crema to finish.