In the past 25 years, large, firm, deep-blue blueberries have transformed from a local specialty to a mass cultivated fruit that has captured the hearts and palates of food lovers all over America. They are excellent cooked in cakes and pies, as well as stewed. Blueberries are fresh in summer, but also available frozen all winter, and these retain the delicious qualities of the fresh variety. For oven-baked recipes you can toss still-frozen berries into the batter, but in crock-baked cakes, the berries must be thawed first.
1Line the bottom of the crock with a round of parchment paper. Coat the paper and one-third of the way up the side of the crock with butter-flavored nonstick cooking spray.
2With an electric mixer, cream the butter and sugar together in a medium-size bowl until fluffy. Add the eggs, one at a time, the vanilla extract, and the sour cream; beat well on medium-low speed for 30 seconds. Add 1 cup of the flour, the baking soda, and the salt and beat on medium-high speed until thick and fluffy, about 30 seconds. Do not overbeat. Sprinkle the blueberries with the remaining 2 tablespoons flour and gently fold them into the mix. Spread the batter evenly in the crock.
3Cover and cook on HIGH until puffed and a cake tester inserted into the center comes out clean, 2 1/4 to 2 1/2 hours.
4Uncover and let stand for 30 minutes before cutting small wedges to serve warm or at room temperature straight out of the crock. To remove, run a knife around the edge inside the crock and lift out the cake in one piece with a large rubber spatula.