Margarita Poke Cake

• All-purpose flour, for dusting
• 1 box vanilla cake mix, plus ingredients called for on box

For the filling

• 1 14-oz. can sweetened condensed milk
• 1/2 cup heavy cream
• 1/3 cup freshly squeezed lime juice
• 1 Tbsp. grated lime zest
• 1 Tbsp. tequila
• 2 drops of green food coloring (optional)

For the frosting

• 1 cup butter, softened
• 5 cups powdered sugar
• 1/4 cup lime juice
• 1/4 cup tequila
• Coarse salt, for garnish
• Limes, cut into half moons, for garnish
• Lime zest, for garnish
• cocktail umbrellas, for garnish