Rinse the spinach in cold water, drain well, and spin or pat completely dry. Trim any tough stems. Peel and thinly slice the garlic.
Heat a large, wide skillet over medium-high heat. Add the olive oil and butter and let the butter foam.
Add the sliced garlic and cook, stirring, until fragrant but not browned, 30–45 seconds.
Add half the spinach and toss with tongs until it begins to wilt, about 30 seconds. Add the remaining spinach and continue tossing until just wilted, 2–3 minutes total.
Season with the salt and black pepper. Cook, stirring, until excess moisture mostly evaporates and the leaves are tender but bright green, 1–2 minutes.
Transfer to a warm plate, taste and adjust seasoning, and serve immediately with lemon wedges for squeezing.