Preheat oven to 350 degrees F and spray 9x5 loaf pan with non-stick spray.

Add butter and granulated sugar to the bowl of a stand mixer.

Mix on medium speed until they are light and fluffy, about 3 minutes. Scrape down the sides a few times while mixing to make sure the mixture is fully incorporated.

Add eggs, one a time, making sure to fully incorporate each egg before adding another.

Add vanilla extract and mix until incorporated.

With the mixer on low gradually add the flour until just combined. DO NOT OVERMIX.

Fold in the diced rhubarb and strawberries into the batter.

Add the cake batter to the prepared loaf pan and sprinkle with coarse sugar.

Add cake to the middle rack of the preheated oven and bake for 55-60 minutes or until a toothpick inserted in the middle comes out clean.

Allow the cake to cool for 5 minutes, run a knife around the edges and turn it out onto a wire rack to cool.

Store refrigerated in an airtight container for up to 3 days.