Preheat the oven to 350 degrees Fahrenheit and line a muffin tin with muffin papers.

In the bowl of a stand mixer fitted with a paddle attachment, cream together the butter, sugar, and vanilla extract until well-combined. Scrape the sides of the mixing bowl using a rubber spatula. Add in the eggs one at a time and beat on medium speed until all of the wet ingredients are combined. Again, scrape the sides of the bowl with the rubber spatula.

In a separate bowl, stir together the flour, baking soda and salt (dry ingredients). Transfer the flour mixture to the bowl with the wet mixture and beat on low speed until the flour is mostly mixed in, then increase the speed to medium or medium high speed until the ingredients are combined.

Add the Greek yogurt to the muffin batter and mix on medium to medium high speed until incorporated into the cake batter.

In a small bowl or measuring cup, mix together the chopped walnuts, brown sugar, cinnamon and a pinch of salt.

Transfer ⅔ of the crumble topping mixture to the bowl with the cake batter and use a rubber spatula to gently fold it in, just until barely incorporated into the dough (don’t over mix).

Fill the paper lined muffin cups ¾ of the way up and sprinkle the top of the batter with the remaining walnut mixture.

Bake on the center rack of the preheated oven for 18-22 minutes, or until the muffins test clean. Move the muffin tray to a wire rack to cool completely.

A great way of determining if a cake is cooked through is by taking its internal temperature using a digital thermometer. Simply insert a thermometer into the center of a muffin. The ideal final temperature for muffins is between 190 and 205 degrees Fahrenheit.

Allow muffins to cool completely before unwrapping one to eat. If you try peeling muffin liners off while muffins are still warm, you’ll lose muffin to the paper.