• Preheat the oven to 400°F, Line two 12-cup muffin pans with cupcake liners and set aside.

Make the muffin batter

• In a large measuring cup or medium bowl, add the almond milk and lemon juice. Set aside and allow to sit for 5 minutes; this creates a vegan buttermilk.
• In a large mixing bowl, whisk together the dry ingredients: the flour, baking powder, baking soda, ground cinnamon, and salt. Set aside.
• In the bowl of a stand mixer (or in a separate large mixing bowl and using a hand mixer), beat together the almond milk/lemon juice mixture, vegetable oil, sour cream, and light brown sugar.
• Gradually beat in the dry ingredients to the wet ingredients.
• Scoop or pour muffin batter into each prepared lined muffin tin, about ¾ of the way full, leaving a little room at the top for the muffins to rise.

Make the streusel

• In a large bowl, whisk together the flour, brown sugar, and ground cinnamon.
• Cut in the cold cubed butter using your hands, until the streusel resembles course crumbles.
• Sprinkle some streusel over the tops of each muffin batter.
• Bake at 400°F for 5 minutes. Then lower the heat to 350°F and continue baking for 12-15 more minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Make top optional glaze

• While the muffins are baking, whisk all of the glaze ingredients in a bowl until smooth and creamy.
• Once muffins have baked and cooled for about 5-10 minutes, drizzle the glaze, if using, over each muffin.