Preheat oven to 180C
Coat bundt cake with butter and dust with flour
Beat brown sugar, baking powder, cinnamon, salt, baking soda, and 2 cups flour in the large bowl of a stand mixer fitted with the paddle attachment on low speed until combined (or use a hand mixer and large bowl)
Add butter (make sure it’s at room temperature) and beat on medium-low speed until mixture resembles coarse sand
Add labneh and vanilla and continue to beat, increasing speed from medium-low to medium as the ingredients begin to incorporate, until batter is thick and smooth, about 1 minute
Add eggs one at a time making sure you beat them well after every addition
Reduce speed to low, add dates, and beat until incorporated, about 30 seconds longer
Bake cake until a tester inserted into the center comes out clean and cake springs back slightly when pressed, 40–50 minutes.