Step 1Heat the oil in a small skillet over medium heat. Fry 3 sage leaves at a time until crisp, 2 to 4 seconds. Use a fork or slotted spoon to transfer the sage to a paper-towel-lined plate. Sprinkle with salt and pepper and let cool. Reserve the sage oil in the pan. (If the sage browns, the oil is too hot; remove it from the heat and let cool for a moment before continuing to fry the sage.)
Step 2Heat a large skillet over medium heat. Use about 1 tablespoon of the sage oil to brush the bread slices on one side. Place as many slices as will fit in a single layer in the skillet and toast until dark golden brown on the oiled side. Repeat to toast all the bread. Transfer the toast to a serving platter.
Step 3Add the remaining sage oil to the large skillet, followed by the garlic, beans and vinegar or lemon juice. Cook for 1 minute, stirring often and using the back of the spoon to smash some of the beans, creating a pleasing mix of whole, smashed and partially smashed beans. Season with salt and pepper.
Step 4Spread each toast with some smashed white beans. Sprinkle with the frizzled sage and serve.