Grease or line a 12-cup muffin tin with muffin liners.
In a large bowl, whisk together the 3 cups gluten free flour, 2 teaspoons baking powder, ¼ teaspoon baking soda, 1 teaspoon cinnamon and 1 teaspoon fine sea salt.
In a medium bowl, whisk together the 1 cup sugar, 1 cup buttermilk, ½ cup unsalted butter, and 2 large eggs until completely combined. Pour into the dry ingredients and gently mix until combined. Fold in the 1 cup strawberries and chopped 2 stalks rhubarb until just incorporated.
Preheat the oven to 375℉. Divide the batter evenly between the muffin cups. Let the batter rest while the oven heats.
Place the muffin tin in the oven and bake for about 20 minutes, until a tester inserted in a muffin comes out clean. Let the muffins cool for 5 minutes in the tin and then turn them out onto a wire rack to cool completely.
Notes
Fresh or frozen rhubarb is fine. If you don’t have fresh rhubarb, frozen works, too. You can add it straight to the batter from the freezer, although you may want to let it soften up for a few minutes so you can chop it up.
Sub maple syrup or honey. I love honey with rhubarb or strawberries (see my strawberry honey jam for more on this!). Swap the granulated sugar with your choice of natural sweetener for a different flavor profile.
Use buttermilk. In my opinion, real buttermilk tastes and performs the best. If you can, use buttermilk in this recipe. If you do need to DIY buttermilk, mix 1 cup of whole milk with 1 tablespoon of lemon juice or vinegar, let it stand for 10 minutes, then add it to the batter.
Make it dairy-free. To make these muffins dairy-free, use 1 cup of your favorite non-dairy milk and stir in 1 tablespoon of vinegar or lemon juice. Let the mixture stand for 10 minutes, then use it in the recipe. Use non-dairy butter for the butter.
Flour substitute. Instead of a gluten-free flour blend, try a mix of ¼ almond flour and ¾ oat flour for a soft, hearty texture (the muffins may be more delicate).
Add nuts. For a bit of crunch, fold in ½ cup chopped walnuts or pecans with the fruit.
Another berry. Swap the strawberries for another berry, such as raspberries or blackberries.
Citrus zest. Rub in the zest of 1 lemon or 1 orange into the sugar to release its oils, then proceed with the recipe.