I started with this recipe from FoodNetwork, but changed it up a little (yogurt instead of sour cream, more topping in layers, little cakes...
For the cake:
8 tablespoons (1 stick) unsalted butter, softened at room temperature
1 cup granulated sugar
2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon baking powder
1/4 teaspoon salt
1 cup yogurt
For the topping:
3/4 cup light brown sugar, packed
3 teaspoons all-purpose flour
3/4 teaspoon cinnamon
3 tablespoons cold unsalted butter, cut into pieces
1 1/2 cup pecans pieces
In a mixer fitted with a paddle attachment, cream the butter until smooth. With the mixer running, slowly add the sugar and mix. Add the eggs and mix until the mixture is light and fluffy. Sift the sifted flour, baking soda, baking powder, and salt together. Working in batches, add them to the butter-sugar mixture, alternating with dollops of yogurt.
Make the topping: In a medium bowl, combine the brown sugar, flour, and cinnamon. Add the butter and, using your fingertips, pinch the ingredients together into a sandy, crumbly mixture. Add the pecans and mix.
Fill the mini-muffin cups 1/3 full of the batter. Add a bit of topping to each cup (you should use half the mixture here). Then fill to 2/3 full with the batter and add the rest of the topping to the top, pressing down a bit to make sure the layers stick together.
Bake until risen and browned, 12-15 minutes. Let cool in the pan.