1. Preheat oven to 350 degrees F. Spray 2 baking sheets with vegetable cooking spray, or line with parchment paper.
2. In a small bowl, sour milk by combining the milk and vinegar. Set aside.
3. In a large bowl, use an electric mixer on medium speed to cream shortening and brown sugar until light and fluffy, about 2 to 3 minutes. Mix in eggs until well incorporated, about 1 minute. Mix in reserved sour milk and vanilla.
4. In a separate bowl, sift together flour, salt, baking soda, and cinnamon. Add gradually to the creamed mixture and mix until thoroughly incorporated. The dough should be smooth, thick, and moist, like a thick cake batter.
5. Drop dough by the tablespoonful onto the prepared baking sheets, about 1 1/2 to 2 inches apart (cookies will spread). Flatten each cookie slightly and make a slight well in the center. Place 1 tsp. jam in the well, then top with an additional 1 tsp. dough. Place one pan of cookies in the oven while you prepare cookies on the second pan.
6. Bake at 350 degrees F for 10 to 12 minutes. The cookies will spread and turn pale gold. Let rest on baking sheet for 1 minute, then transfer to a rack to cool. Serve at room temperature. Store in an airtight container, with waxed paper between layers.
Source: fresh magazine May, June 2010