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Place a rack in the middle of the oven and preheat the oven to 350°F.
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Lightly grease 8 wells of a standard muffin tin, or line them with muffin papers and lightly grease the papers; this will ensure that they peel off the muffins nicely.
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To make the muffins: In a medium bowl, combine the flour, baking sugar alternative, baking powder, nutmeg, and salt. Set aside.
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In a separate mixing bowl, combine the melted butter, vegetable oil, egg, milk, and vanilla, whisking until smooth.
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Add the dry ingredients to the wet ingredients, stirring until combined. Fold in the blueberries.
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Divide the batter evenly among the prepared muffin cups.
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Bake the muffins for 20 to 24 minutes, or until they're a pale golden brown and feel set on top.
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Remove the muffins from the oven and let them cool for a couple of minutes, or until you can handle them. While they're cooling, prepare the topping.
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To prepare the topping: Put the melted butter into a small bowl and combine the baking sugar alternative and cinnamon in a separate small bowl.
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Transfer the muffins to a cooling rack. Dip the top of each muffin into the melted butter. Return them to the rack for a minute or so before dipping in the topping to finish.
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Serve the muffins warm, or cool on a rack and wrap airtight. Store for several days at room temperature; freeze for longer storage.