1cupfrozen or fresh blueberriesif using frozen, keep them unthawed and add them frozen
about 1/3 cup jamuse your favorite flavor, blueberry is best
3tablespoonssugarfor sprinkling (I used 1 tablespoon turbinado and 2 tablespoons granulated)
For the Glaze
¼cupunsalted buttermelted
about 1 cup+ confectioners’ sugarsift if it’s particularly lumpy
¾teaspoonvanilla extract
Instructions
Coffee Cake
Preheat oven to 400F. Spray a 9-inch round cake pan with floured cooking spray, or grease and flour the pan; set aside.
To the bowl of a stand mixer fitted with the paddle attachment (or a large mixing bowl and hand mixer), add the flour, 3/4 cup granulated sugar, baking powder, baking soda, and mix momentarily to incorporate.
Add the egg, buttermilk, 1/4 cup butter, vanilla, and beat for 1 minute on medium-low speed. Stop, scrape down the sides of the bowl, and beat for 1 minute on medium speed.
Turn batter out into prepared pan.
Using a spoon, dollop the jam over the batter surface in teaspoon-sized mounds, making about 15 mounds (doesn’t have to be precise; some jam blobs will be bigger than others and that’s fine). Using a table knife, lightly marble the jelly into the top surface of the batter, going up and back in a zigzag pattern a couple times.
Sprinkle blueberries evenly over the batter (it looks like a ton). Sprinkle evenly with 3 tablespoons sugar over the blueberries.
Bake for about 30 minutes or until center is set and not jiggly, and a toothpick inserted in the center comes out clean, or with a few moist crumbs dangling, but no batter. Note – I turned my oven down to 375F in the last 5 minutes of baking because the edges were getting a little too browned for my liking before the center had fully set; watch your cake in the last 5 to 10 minutes of baking and turn down oven if necessary, or tent with foil.
Allow cake to cool in pan for about 10 minutes before turning out onto a wire wrack to cool completely (I invert it onto a cutting board, then slide it off the cutting board and onto the rack with the blueberry side up).
While the cake cools, make the glaze.
Glaze
Melt the butter in a small, microwave-safe bowl, about 45 seconds.
Add about 1/2 cup sugar, vanilla, and whisk to combine. Continue adding sugar and whisking until smooth and desired glaze consistency is reached. If you accidentally make it too thick, adding a tiny splash of milk or cream will thin it out.
Drizzle glaze over cake in big ribbons, going up and back, over the surface (the photos show the glaze much skimpier because I wanted the blueberries to be visible, but I used all the glaze after the photos were completed).
Notes
If you have extra glaze, it will keep airtight in the refrigerator for at least 1 month. I store cake airtight at room temperature where it stays fresh for 4 days. Store in the refrigerator (due to the glaze) if desired.