Preheat the oven to 350°F (175°C) and line a muffin tin with paper liners.
Peel and cut the sweet potatoes into small chunks, then steam them for 15-20 minutes until they are soft. If you are using canned sweet potato puree, you can skip this step and the next one too!
Cool the steamed sweet potatoes under cold running water, and let them drain dry. Mash then a bowl with a potato masher, or inside of a food processor until smooth. Measure out 1 ½ cups of mashed sweet potato to use for this recipe. Give any leftover mashed sweet potato as a well deserved treat for your doggo (or use them as a bed to serve some vegan fried chicken over). In a large mixing bowl, combine the mashed sweet potatoes, canola oil, brown sugar, unsweetened plant-based milk, vegan yogurt, and vanilla extract. Mix until well combined.
Sift in the all-purpose flour, baking powder, baking soda, cinnamon, cardamom, nutmeg, and salt. Stir with a rubber spatula until just combined. Be careful not to overmix.
To prepare the maple pecan streusel, in a small bowl, mix the all-purpose flour, chopped pecans, maple syrup, cinnamon, salt, and melted vegan butter until the mixture forms a crumbly texture.
Using a lightly oiled quarter-cup measuring cup or an ice cream scoop, spoon the batter into the prepared muffin tin, filling each cup about three-quarters full. Sprinkle the maple pecan streusel evenly over the top of each muffin.
Bake in the preheated oven for 22-26 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the tin for five minutes before transferring them to a wire rack to cool. Serve warm or at room temperature.