Preheat the oven to 350 °F and line a cupcake/muffin pan with cupcake liners.
In a medium bowl, whisk together 1 1/4 cups flour , 1 1/4 tsp baking powder, 1/2 tsp baking soda and 1/2 tsp salt.
Set flour mix aside.
In the bowl of an electric mixer, beat 2 eggs with the whisk attachment on medium speed (15-20 seconds).
Add 3/4 cup sugar and continue to beat on medium speed (30 seconds)
Add vanilla and oil and beat on medium speed (1 minute)
Reduce mixer speed to medium/low and slowly add about half of the flour mixture.
Now add half of the milk, then the rest of the flour mix and the rest of the milk.
Beat until just combined and smooth, scraping down the sides of the mixing bowl
Add the marshmallows and fold into the mix
Pour batter into a lined muffin pan and fill to about 3/4 full
Bake for 12 -14 minutes at 350 °F.
Let them cool in the pan for a couple minutes, then remove