Step 1

Spray a 7-inch cake pan with nonstick cooking spray and line the bottom with parchment paper. Spray parchment paper with nonstick cooking spray. Set aside.

Step 2

In a large mixing bowl, beat the butter until fluffy. Add sugar and beat again. Add eggs and one extra egg yolk and beat until fluffy. Add yogurt and vanilla extract and beat to combine.

Step 3

Combine dry ingredients (flour, baking powder, cinnamon, salt, cardamom, nutmeg) in a separate bowl, then slowly beat them into the wet ingredients, scraping down the sides of the bowl as needed. Set aside while you make topping.

Step 4

In a small bowl, combine melted butter with brown sugar and chopped rhubarb. Spread mixture into the bottom of the prepared cake pan.

Step 5

On top of rhubarb mixture, spread cake batter into an even layer (batter will be thick).

Step 6

Cover pan with a paper towel and then wrap tightly with foil.

Step 7

In the bottom of a 6-quart Instant Pot insert, add 1 cup of cold water.

Step 8

Place covered cake pan on top of steamer insert and carefully place it in the Instant Pot.

Step 9

Cover and turn valve to seal. Set Instant Pot to manual high pressure for 60 minutes.

Step 10

When the timer goes off, let the Instant Pot naturally release pressure buildup for 10 minutes before doing a quick release.

Step 11

Remove foil and paper towel and run a butter knife around the edges of the cake pan. Place a heat-safe plate that has a rim (not a cake stand!) over the cake pan. Holding the plate in place, carefully flip the plate and pan over. Slowly remove cake pan from cake. Slice and serve warm or at room temperature.