Preheat your oven to 350°F.
In a bowl, combine the raspberries and brown sugar; set aside.
1 cup fresh raspberries, 3 tbsps. light brown sugar
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. In a separate small bowl, whisk the egg, sour cream, butter, and vanilla. Gently stir the wet ingredients into the dry ingredients just until moistened. (The batter will be dense.)
1 cup all-purpose flour, 1/3 cup granulated sugar, 1/2 tsp. baking powder, 1/4 tsp. baking soda, 1/8 tsp. table salt, 1 large egg, 1/2 cup full-fat sour cream, 3 tbsps. butter, 1 tsp. vanilla extract
Spoon half of the batter into a greased and floured 8-inch round baking pan, making sure you completely cover the bottom (it may seem like there isn’t enough batter, but there is. Using a small offset spatula helps spread it evenly). Top with the raspberry mixture. Then, spoon the remaining batter over the raspberries. (Again, the batter may appear insufficient; simply swirl it around gently, you don’t need to completely cover the raspberries.) Finally, sprinkle with almonds.
¼ cup sliced almonds
Bake for 20–25 minutes or until a toothpick inserted near the center comes out clean. Cool the cake on a wire rack for 15 minutes before removing it from the pan. During cooling, carefully run a sharp knife around the edges to loosen the cake. Flip it out of the pan and set it right side up.
In a small bowl, combine the icing ingredients. Drizzle the icing over the coffee cake and serve.
1/4 cup confectioners' sugar, 1-1/2 tsps. whole milk, 1/4 tsp. vanilla extract