In a small bowl with a whisk, or in a jar with a tight-fitting lid, add the vegetable oil, red wine vinegar, sugar, dried mustard, poppy seeds, and salt to taste (I like 1 teaspoon). Stir or shake to combine.
In a small skillet over medium-low heat, melt the butter. Add the pecans and toast until fragrant, stirring often to prevent scorching, about 10 to 15 minutes. Drain on paper towels.
In a large bowl, add spinach, strawberries, and pecans. Drizzle with dressing and toss until evenly coated.
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Notes
Olive oil: The original dressing was made with vegetable oil, so feel free to substitute that if you prefer.
Sugar: 1/4 cup sugar makes for a super sweet vinaigrette, so feel free to add less to taste.
Butter: Toasting the pecans in butter takes them right over the top. Substitute olive oil if you're preparing a vegan salad or prefer that.
Pecans: To toast the pecans, in a dry skillet over medium-low heat, melt the butter or heat the olive oil. Add the pecans and toast until fragrant, stirring often to prevent scorching, about 10 to 15 minutes.
Spinach: If you prefer, substitute half the spinach for field greens.
Yield: This recipe makes about 12 cups of salad. It's enough for 6 large servings of 2 cups each, such as for lunch, or 12 servings, 1 cup each, for a party or buffet.
Storage: Store leftover salad in the refrigerator for up to 4 days. For lunches and meal prep, store the components separately.