Preheat your oven to 400°F. While it heats, hull and dice the strawberries into 1/4-inch pieces, then pulse them in a food processor until chunky but not completely smooth—you want some texture remaining for flavor bursts in each bite. Sift the powdered sugar to remove any lumps, which will help create a smooth glaze later. Ensure your egg is at room temperature, as this helps it incorporate better with the butter and sugar, creating a lighter, airier batter.

In a medium bowl, cream together the butter and sugar for about 2 minutes until light and fluffy. This step incorporates air into the batter, which is essential for a tender crumb. Add the room-temperature egg and beat until fully combined and pale, about 1 minute. Stir in the vanilla extract, then add the buttermilk and pulsed strawberries, mixing until just combined. I find that folding gently at this stage rather than overmixing helps keep the strawberry pieces intact and distributed evenly throughout the batter.

In a separate bowl, whisk together the cake flour, all-purpose flour, baking soda, baking powder, salt, and ground nutmeg. This ensures the leavening agents and salt are evenly distributed. Gently fold the dry ingredient mixture into the wet mixture from Step 2 until just combined—do not overmix, as this will develop gluten and result in tough donuts. The batter should be thick and chunky with visible strawberry pieces. Transfer the batter into a piping bag and snip off about 1/2 inch from the corner to create a small opening for piping.

Lightly grease a donut tin with non-stick cooking spray or butter. Using the piping bag from Step 3, fill each donut cavity about halfway with batter—this allows room for the donuts to rise without overflowing. Bake in the preheated 400°F oven for 7-8 minutes, until the tops are set and a toothpick inserted into a donut comes out clean or with just a few moist crumbs. The donuts should be light golden and spring back slightly when lightly touched. Remove from the oven and let cool in the tin for 2-3 minutes before turning out onto a wire rack to cool completely.

While the donuts cool, whisk together the sifted powdered sugar and milk in a small bowl to create a smooth glaze. Start with 2 tablespoons of milk and add more as needed, one teaspoon at a time, until the glaze reaches a consistency that's pourable but still clings to the donuts—it should be thicker than milk but thinner than cake batter. Once the donuts have cooled completely, dip the top of each donut into the glaze, allowing excess to drip off, then place back on the wire rack. I prefer to glaze donuts while they're still slightly warm so the glaze sets beautifully and looks glossy.

Allow the glazed donuts to set for 20-30 minutes at room temperature, during which time the glaze will firm up and become glossy. These donuts are best enjoyed the same day they're made, when the cake is still tender and fresh. They're perfect for a Valentine's Day breakfast or dessert celebration.