Preheat oven to 350°F. Spray a 9×13-inch baking dish with baking spray or line with parchment paper. Set aside.
In a small bowl, stir together granulated sugar and cinnamon for the swirl mixture. Set aside.
In a medium bowl, whisk together flour, baking powder, kosher salt, and cream of tartar.
In a stand mixer (or using a hand-held mixer), cream together butter and granulated sugar on medium speed until light and fluffy, about 2-3 minutes.
Add eggs, milk, vegetable oil, and vanilla extract. Mix on low speed for about 1 minute, just until combined.
Gradually add the dry mixture to the wet ingredients, mixing on medium speed for about 30 seconds until just incorporated. Do not overmix.
Pour half of the batter into the prepared pan and spread evenly.
Sprinkle half of the cinnamon-sugar mixture evenly over the batter.
Add the remaining batter and gently spread it out, then sprinkle the remaining cinnamon-sugar mixture evenly over the top.
In a small bowl, combine the brown sugar, flour, and cinnamon. Add the cold, cubed butter and use your fingers, a fork, or a pastry cutter to create pea-sized crumbs. Sprinkle this evenly over the batter for a sweet, crunchy layer.
Bake for 35-40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. If the top is browning too quickly, loosely cover with aluminum foil for the last 10 minutes of baking.
Allow the cake to cool in the pan for 10-15 minutes before adding the glaze.
To make the glaze, in a small bowl, whisk together the confectioners’ sugar and milk until smooth. Add more milk, a few drops at a time, if a thinner glaze is desired.
Drizzle glaze over warm cake.
Slice and serve warm or at room temperature.