Blueberry Muffin Bundt Cake

For the Cake
1 Cup unsalted butter, softened
2 Cups sugar
3 Large eggs
1 Tablespoon vanilla extract
2 3/4 Cups all purpose flour
2 Teaspoons baking powder
1/2 Teaspoon baking soda
1/2 Teaspoon salt
1 1/4 Cup buttermilk
Zest of 2 lemons
1 Pound fresh blueberries
For the Buttermilk Glaze
3 Tablespoons buttermilk
1 Cup powdered sugar
For the Oat Crumble Topping
2 Tablespoons butter
2 Tablespoons brown sugar
3 Tablespoons flour
2 Tablespoons oats
2 Tablespoons sliced almonds

For the Cake
Preheat the oven to 325�F. Spray a standard 12-cup bundt pan with non-stick cooking spray and sprinkle lightly with flour. In the bowl of an electric mixer, cream the butter and sugar together until light and fluffy. Then beat in the eggs and vanilla. Mix the flour, baking powder, baking soda, and salt in a separate bowl. Turn the mixer on low and slowly add the flour and buttermilk, alternating each, until all incorporated. Finally beat in the lemon zest before turning the mixer off. Use a spoon the stir in half the blueberries.
Pour the batter into the prepared bundt pan and sprinkle the remaining blueberries over the top. Bake for 60-80 minutes, until a toothpick inserted into the center comes out clean. Remove the cake from the oven and allow it to cool for at least 20 minutes before flipping out onto a cooling rack. DO NOT try flipping the cake any earlier than 20 minutes, or the cake will stick. Promise! Waiting 30+ minutes is safer.
Once the cake is cooling on the rack, mix the oat crumble. Add all the ingredients to a small bowl and pinch with your fingers to blend the ingredients and break into small pieces. Sprinkle the mixture over a baking sheet and bake in the heated oven for 5-10 minutes. Cool on the baking sheet before proceeding.
For the glaze, whisk the buttermilk and powdered sugar in a small bowl. Drizzle the glaze over the cake and immediately sprinkle the oat crumble over the top of the cake before the glaze dries.
NOTE: A couple people have mentioned the top sticking in the bundt cake in this recipe. I have made this cake quite a few times and have never had this happen. The main thing to focus on, for a cake that flips out perfectly, is to spray (or grease) the bundt pan thoroughly (meaning every nook and cranny) then flour it well. After it comes out of the oven DO NOT flip the cake any earlier than 20 minutes after baking. If your cake still feels hot after 20 minutes, that means your bundt pan is very well insulated. In this case, I would wait 35-45 minutes before flipping to make sure the cake has cooled to close to room temperature. You could even place the cake in the fridge to speed up the cooling time.