Grease and flour an appropriately sized dish for Instant Pot.

Mix the flour, baking powder, and salt in a small bowl. Reserve 2 tablespoons for Step 6.

Add zest, sugar, and room temperature butter to mixer and beat until thoroughly combined, scraping down the sides when necessary.

Add egg and vanilla to mixer and combine

Adding 1 cup at a time, start with the flour mixture and buttermilk to the sugared butter in the stand mixer. Incorporate completely before adding another cup one at a time. Remove mixer bowl

Lightly toss the blueberries with reserved flour and gently fold into batter

Pour 2/3 cup of water in Instant Pot with rack. Spoon half of batter into greased/floured dish and transfer to Instant Pot.

Set Instant Pot to High Pressure and Manual for 30 minutes

When done, quick release the pressure then immediately remove the cake. 

Allow condensation to dissipate completely before transferring to a serving dish