Preparation

• In a 2-quart saucepan over medium heat, combine the beans, olive oil, onion and garlic powders, chipotle, oregano, and 1/4 cup water. Cook, mashing with a potato masher, until the beans are hot, well mashed, and thickened to a spreadable consistency, about 3 minutes. Season to taste with salt.
• Stack the tortillas 3 at a time and prick through the stack in several places with a fork to prevent the tortillas from puffing up as they fry. Add enough oil to an 8- to 9 inch skillet to measure 1/2 inch deep (about 1 cup) and heat over medium-high heat until shimmering hot. Add a tortilla and cook, flipping 3 to 4 times with tongs and gently holding the tortilla under the oil until it’s crisped and golden-brown, 2 to 3 minutes total. Transfer to a paper-towel-lined plate to drain. Repeat with the remaining tortillas, adding more oil as necessary.
• Serve the tostadas slightly warm or at room temperature, each spread with some of the beans and drizzled with a little crema or a dollop of sour cream, if you like.