01 -
Preheat oven to 175°C. Line a standard muffin tin with paper liners and set aside.
02 -
In a medium bowl, whisk together flour, sugar, and cinnamon. Add butter pieces and incorporate using a fork or pastry blender until the mixture forms coarse crumbs. Set aside.
03 -
In a separate medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
04 -
In the bowl of a stand mixer with paddle attachment, beat softened butter, oil, and granulated sugar together until smooth and creamy.
05 -
Add eggs one at a time, beating thoroughly after each addition to ensure complete integration.
06 -
Reduce mixer speed to low. Pour in sour cream and vanilla extract, mixing until just combined.
07 -
Gradually add the dry flour mixture to the wet ingredients. Mix until just combined, taking care not to overwork the batter. Finish with a spatula to ensure all ingredients are fully incorporated from the bottom of the bowl.
08 -
Spoon a generous tablespoon of batter into each muffin cup. Sprinkle a portion of the streusel over the batter. Divide remaining batter among the cups, then top each with remaining streusel, distributing evenly.
09 -
Transfer to the preheated oven and bake for 15 to 20 minutes, or until a toothpick inserted into the center of a muffin emerges clean.
10 -
Carefully remove the muffin tin from the oven and transfer each muffin to a wire rack to cool completely before serving.