This recipe is from Classic German Baking and recommended by my friend, Hubertus Funke
Preheat the oven to 350 degrees. Line a 9 x 13" metal baking pan with parchment paper, letting the sides hang over the edges to function as sling after baking.
Cut the butter into cubes and place in a large bowl. Add the sugar, flour, salt, and cinnamon. Work together with your fingertips until the mixture is well combined and crumbly with lima bean and pea-sized clumps (I used a food processor with the blade on the chop cycle and it worked fine). Place in the refrigerator until ready to use.
Drain all the liquid from the cherries into a small saucepan, reserving the cherries. Place 3 tablespoons of the juice in a small bowl. Bring the remaining liquid in the saucepan to a boil over medium-high heat. While bringing to a boil, whisk the cornstarch into the bowl of reserved juice until no lumps remain.
When the cherry juice starts to boil, whisk the cornstarch mixture into the pot. The juice will almost immediately start to thicken. Remove the pot from the heat and continue to whisk until the mixture is smooth. Fold the reserved cherries into the hot, thickened juice and set aside to cool. (Hubertus usually uses a dark rum to make that cornstarch mix).
In the bowl of a stand mixer fitted with the flat beater attachment, cream together the butter and sugar until light and fluffy. Beat in the eggs, one at a time. Then beat in the vanilla extract. In a separate bowl whisk together the flour, baking powder, and salt. Beat the flour mixture into the butter mixture., scrape down the sides, and then beat in the milk. Scrape the batter into the prepared pan.
Distribute the cherries and thickened juice evenly all over the cake batter. Sprinkle the Streusel mixture over the cherries (breaking up any clumps). Place the pan in the oven and bake for 45 to 50 minutes or until the Streusel is light-golden.
Remove the pan from the oven and let it cool on a rack. The cake can be served slightly warm or at room temperature. The cake will keep at room temperature, loosely wrapped in plastic wrap for a few days.