Preheat oven to 350F and grease an 8x8" baking dish.

In the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl with an electric hand mixer), combine butter, sugar, and brown sugar. Beat until light and fluffy.

Add eggs and vanilla extract, mixing to incorporate, scraping down the sides of the bowl as needed.

Add flour to the bowl, mixing on low speed just until combined.

Add milk, mixing on low speed until incorporated. Set aside.

Prepare streusel by combining pecans, brown sugar, flour, ground cinnamon, and butter in the bowl of a food processor. Pulse until the mixture is the consistency of coarse crumbs.

Spread half of the batter into prepared pan. Top batter with half of the streusel, followed by diced pears. Add remaining batter on top of the pears, followed by the remaining streusel.

Bake in preheated oven for 45 minutes, or until a toothpick inserted in the center comes out clean.

Let cool for a few minutes before slicing and serving warm.