Preheat oven to 350°F. Line a muffin tin with cupcake liners.
Place 2 and 1/4 teaspoons lemon juice in a measuring cup. Add enough milk to the measuring cup to equal 3/4 cup; let sit for a few minutes.
Puree the pears in a food processor or blender until completely smooth.*
In a medium-sized mixing bowl, whisk the flour, baking soda, spices, and salt together; set aside.
In a stand mixer fitted with the paddle attachment, beat the butter and both sugars together until combined. Mix in the egg, egg yolk, and vanilla. Stir in the pear puree and remaining 1 and 1/2 teaspoons lemon juice.
With mixer on low, alternate adding the dry ingredients with the milk mixture until just combined; do not overmix.
Pour batter into cupcake liners, about 3/4 full. Bake for 15-18 minutes, or until a toothpick inserted in the center comes out with few crumbs attached. Allow cupcakes to cool for 15 minutes before transferring to a wire rack to cool completely.