Cream the Butter and Sugar: In a large bowl, use an electric hand mixer (or a stand mixer fitted with the whisk attachment) to beat the softened butter, softened coconut oil, and granulated sugar together on medium-high speed until light and fluffy, about 3–4 minutes.

Note:I used softened coconut oil, not melted. To achieve softened coconut oil, only melt slightly in the microwave. You could also use all butter and omit the coconut oil, if desired. The purpose of the coconut oil is to help the cupcakes remain soft and tender even after sitting on the counter or in the fridge.

Add the Eggs: Add eggs one at a time, beating on high speed after each addition until fully combined. The mixture will become light and fluffy.

Mix in Yogurt and Starter: Add plain yogurt and the potato flake sourdough starter. Mix on low speed just until everything is blended.

Note: Avoid using cold yogurt and starter. If the yogurt and starter are cold, it could cause the coconut oil to solidify, causing a grainy looking texture. If this happens, it will likely reincorporate after fermentation, but it's just easier to avoid.

Cover and Ferment: Cover the bowl with plastic wrap and allow to ferment at room temperature for 8–10 hours or overnight.

After making the batter, it is a good time to go ahead and make the strawberry puree. Doing it at this stage will allow it too cool in the fridge and be ready for the next step after fermentation.

Note: If you have a stainless steel saucepan, use it for this step, so that you do not have to take the puree out of the sauce pan to blend it with the immersion blender.

In a medium saucepan, combine 400 grams of strawberries with 2 tablespoons of sugar. Cook over medium-low heat until soft and juicy, about 8–10 minutes.

Use an immersion or regular blender to puree the mixture until smooth.

Return to the pan and reduce over medium-low heat until thickened to about 1/2 cup. Stir frequently to avoid burning. Let cool completely in the fridge until ready for the next step.

After fermentation, finish adding the rest of the ingredients.

Preheat Oven: Set your oven temperature to 350°F (175°C). Line a muffin tin with parchment cupcake liners.

Prepare strawberries: Wash, hull and diced strawberries. You will need 3/4 cup of strawberries ready to add to the batter.

Finish the Batter: To the fermented mixture, add 1/4 cup of strawberry puree (reserving the rest for the frosting), baking soda, baking powder, vanilla, salt, and food coloring if using. Mix gently to combine.

Note: It's recommended to sift the baking soda and baking powder to avoid clumps.

Fold in Strawberries: Use a spatula to fold in the 3/4 cup diced strawberries.

Bake: Bake for 18–22 minutes or until the tops are golden brown and a toothpick comes out clean.

Cool Completely: Let cool in the tin for 5 minutes, then transfer to a wire rack to cool fully before adding the frosting.

While the cupcakes cool, prepare the frosting.

In a stand mixer with a whisk attachment, beat softened butter and 1/4 cup of cooled strawberry puree on medium-high speed until fluffy.

Add vanilla, food coloring (if using) and powdered sugar, starting with 1 cup, adding 1 cup at a time to avoid it from shooting out when mixing. Start on low speed, then increase to medium-high and beat until smooth.

Store in an airtight container in the fridge. Let come to room temperature before serving.