Preheat oven to 350°F (180°C). Grease a 9x9-inch pan and line with parchment if you like. In a medium bowl, whisk together 2 cups flour, baking powder, baking soda, and salt.

In a large bowl, beat 1/2 cup butter and 3/4 cup sugar on medium speed until light and fluffy, about 3 minutes.

Beat in eggs one at a time, then 1 teaspoon vanilla. On low speed, alternately add the flour mixture and 1 cup buttermilk, starting and ending with flour. Mix just until combined.

Toss 1 1/2 cups cranberries with a teaspoon of the flour, then fold gently into the batter.

For the streusel, combine 1/2 cup flour, brown sugar, cinnamon, and salt. Cut in 4 tablespoons cold butter until crumbly. Spread half the batter into the pan, sprinkle with half the streusel, top with remaining batter and streusel. Bake 45 to 50 minutes, until a toothpick comes out clean.

Cool in the pan 10 minutes, then lift out or slice. Cool at least 20 more minutes before slicing into squares.