In a large bowl, whisk the eggs with the milk and season with salt and pepper. In a large cast-iron or nonstick ovenproof skillet, melt the remaining 1 tablespoon of butter in the olive oil; swirl the pan to coat the bottom and side. Add the garlic and cook over low heat, stirring occasionally, until golden, about 4 minutes. Add the spinach and stir with tongs until slightly wilted. Drain off any liquid and spread the spinach evenly in the pan and sprinkle with the lemon juice.