1Heat oven to 375°F. Place paper baking cup in each of 12 jumbo or 24 regular-size nonstick muffin cups. In small bowl, mix topping ingredients with fork until crumbly; set aside.
2In large bowl, mix 4 cups flour, the baking soda and 1 teaspoon salt. In another large bowl, beat eggs with electric mixer on medium speed about 2 minutes or until frothy. Add 2 cups granulated sugar and the oil; beat until creamy. Add sour cream, lemon peel, 2 tablespoons lemon juice, the lemon extract and vanilla; mix well. Stir in flour mixture just until blended. Fill muffin cups 3/4 full. Divide crumb topping evenly over batter in each muffin cup.
3Bake jumbo muffins 22 to 28 minutes, regular-size muffins 20 to 22 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes; remove from pan. Cool completely.
4In small bowl, mix glaze ingredients until well blended. Drizzle over muffins.