Preheat oven to 350 degrees F. Line 24 muffin cups with cupcake liners.: When you enter the kitchen you'll notice a quick warmth as the oven comes to temperature, and that preheated air helps the cupcakes rise evenly. Preheating ensures the batter begins baking immediately, creating a tender crumb rather than a flat, dense cake. A common mistake is putting batter into a cold oven which leads to poor texture. If your oven runs hot, use an oven thermometer to check the regulated 350 degrees F temperature and rotate the pan halfway through baking for even color and rise.
Place all cupcake ingredients into a large mixing bowl and mix well with an electric mixer for 2-3 minutes. Fill cupcake liners 2/3 of the way full with cupcake batter.: The sound of the mixer changes as the batter blends, shifting from a slosh to a smooth hum, and you'll see the batter become glossy and even. This mixing time hydrates the dry mix and distributes the strawberry Jell-O and strawberry puree throughout the batter so each cupcake carries fruit flavor. Overmixing will develop gluten and toughen the crumb, so stop once the batter is homogeneous. Use an ice cream scoop for consistent portioning, and fill liners about two thirds full to achieve domed tops without overflow.
Bake for 14-16 minutes or until a toothpick inserted into the center comes out clean. Remove from the oven and allow to cool completely prior to frosting.: As the cupcakes bake you'll notice an inviting, jammy aroma rising from the oven while the tops turn a pale golden hue tinted with pink. The toothpick test confirms internal doneness; a few moist crumbs are fine, but batter on the pick means more time is needed. Cooling completely is crucial so the butter and cream cheese in the frosting do not melt and slide off. A common misstep is frosting warm cupcakes which results in collapsed swirls and messy presentation. Set the cooled cupcakes on a wire rack so air circulates underneath, preventing sogginess.
Cream together butter and cream cheese until well combined, light and fluffy – about 2 to 3 minutes, scraping down the sides of the bowl as needed. Add in one cup of powdered sugar and mix until well combined. Repeat with remaining powdered sugar, one cup at a time.: When you begin creaming, the texture should transition from chunky and cold to smooth and billowy, with the mixer beating in tiny air pockets that make the frosting light. Scraping down the bowl ensures no pockets of dense cream cheese remain, which would create uneven sweetness. Adding powdered sugar gradually prevents dust clouds and helps control sweetness and thickness. Watch for the frosting turning overly stiff, which can happen if you use very cold butter or too much sugar all at once; if that occurs, a tablespoon of strawberry puree or a touch of milk will soften it.
Add in strawberry puree, vanilla extract and jam. Beat with an electric mixer until well combined. If a thicker frosting is desired, add more powdered sugar, 1/4 cup at a time. If a thinner frosting is desired, add in more strawberry puree, milk or cream, one tablespoon at a time, mixing well, until desired consistency is reached. Frost cupcakes with an offset spatula or by piping on. Top each cupcake with a fresh strawberry if desired.: As you fold in the strawberry puree and jam, the frosting will bloom into a fragrant, slightly glossy pink, releasing sweet berry aromas. The mixing sound softens and the texture should be creamy, not runny. Adjusting consistency is about feel, slight changes alter pipeability and mouthfeel, so add sugar or liquid slowly and taste as you go. A common error is over thinning, which causes frosting to slide; if that happens, chill the bowl briefly and rewhip. When piping, watch for peaks that hold shape; using an offset spatula gives a rustic look, while piping yields elegant swirls perfect for gifting.