Spinach Salad with Roasted Grapes and Warm Bacon Vinaigrette

Name: Spinach Salad with Roasted Grapes and Warm Bacon Vinaigrette
Ingredients: 2 cups seedless red grapes; 1 teaspoon extra virgin olive oil; Salt , to taste; Ground black pepper , to taste; 1/2 cup raw walnuts; 8 slices bacon , cut into 1/2 inch pieces; 6 cups baby spinach , long stems removed; 3 ounces crumbled feta; 1/4 cup reserved bacon grease; 1/4 cup shallot , finely chopped; 1 teaspoon Dijon mustard; 2 tablespoons apple cider vinegar; 1 teaspoon sugar; 1/4 teaspoon salt; 1/8 teaspoon ground black pepper