Preheat the oven to 350°F. Coat the muffin tin with cooking spray or butter (optional: muffin paper liner).
In a separate bowl: combine flour, sugar, lemon juice and COLD butter. Use a pastry cutter or your hand to mix until it begins to form coarse crumbs.
In a large bowl: beat the sugar and eggs together. Then add the half & half or whole milk, oil, vanilla extract, lemon juice and lemon zest. Mix well.
Once the mixture is uniform, add in the flour, baking powder and salt. Combine using a mixer mix.
Use an ice cream scooper to measure even portions. As you carefully place each scoop of batter in the muffin tin (should be exactly 12 scoops). Sprinkle the streusel mixture atop the batter.
Bake for 20-22 minutes or until golden brown. Let the muffins cool in the tin for about 10 minutes and then transfer them to a baking rack to finish cooling completely.