In a small bowl, combine butter, sugar, salt and flour and blend with your fingers until combined. Mix in nuts. Cover and chill while you make the cake batter.
Preheat oven to 350°F. Butter a 9-inch cake or springform pan, line the bottom with parchment paper and set aside.
In a small bowl, whisk to combine all-purpose flour, rye flour, baking powder and salt.
In a large bowl, combine butter and sugar and cream with a handheld mixer until light and fluffy, 3- 5 minutes. Beat in egg, buttermilk and vanilla extract until combined (mixture may look curdled, that’s fine). Add dry ingredients and mix until just combined.
Pour batter into prepared pan and arrange the cherries in an even layer on the surface, cut side down. Sprinkle cherries with lemon juice then crumble the walnut streusel on top.
Bake for 10 minutes, then reduce heat to 325°F and continue to bake for a total of 55-65 minutes, or until the top is golden brown and a toothpick inserted into the cake (not a cherry!) comes out clean.
Set aside to cool completely. Run a knife around the edge of the springform pan, then release sides and carefully remove cake. Enjoy!
